I think part of the problem with your question is the use of the word 'improper'. Most cases of concern are the result of conflicts of interest which you specifically exclude in your question.
Maybe replace the word improper and replace it with 'inappropriate' and I think you're in much clearer waters..... I can think of a number of cases when the selection wasn't improper per se might it might not have been 100% appropriate!

I'll bite - what makes a conflict of interest "significant"? For example, I'm helping at an upcoming event where the RO for the opti course has 2 kids in a fleet of >50 boats. Is this substantial? Would it be if there are 100? For the record, the RO has swapped onto a course where he has zero conflict, appearance or actual.

David, I used “improper” because that is the word used by RRS 62.1(a) under redress.   If it doesn’t rise the level of improper, what avenue does a party have to raise the issue?

Carl, like “improper” above, I chose “significant” because that is the word used in RRS 63.4(b)(2). 

FWIW .. my OP isn’t trying to be a gotcha question. Mostly in my experience the above appointments are made via email, phone call, text, or a handshake at the bar before the event, without formal documentation or notice.

So the question rephrased is, “When, or under what circumstances, do these appointments require something more in the form of process, formal documentation and/or notice to the public or competitors .. and lacking that process/notice/documentation … the appointments were made improperly and thus become subject to challenge or being invalidated?”

PS: The answer might be that there are none, except when these requirements are detailed in the event’s Conditions (by the Class, Regulations or event docs). 

Angelo- I know you had a reason to use the words you did, and you do it well. Unfortunately for me that doesn't tell me what comprises "significant" and since I studied accounting lo these many years ago I've always kinda wondered defines "materiality" as well. Kinda nebulous, which leaves it open to interpretation, which usually leads to some kind of acrimony. I don't like acrimony, myself. I'm ... not a fighter. 😁

Carl - in case you are not aware of it WS has a document available that gives guidance in assessing conflict of interest titled “Guideline for assessing a Conflict of Interests for Race Officials”.  It is available on the resources page https://www.sailing.org/our-sport/race-officals/resource-centre/.

Greg- Thank you, I was not. WS is good at hiding things on the website, as are some MNAs that are not to be mentioned. A 10+ page documentation of what should be common sense does not surprise me. In any event, thank you for pointing me to it, I will have a look and see how it applies to a local event.

My view: sailors have the right to be informed about everything governing the event.

Publishing PC components
It's common practice to publish the composition of the PC. Logic. 
Otherwishe, during a hearing, when asking the parties wether they consent to the members, a logical reply can be "how should i know, if you introduce yourself just now?" (M2.3) 
Not posting the composition of the PC panel makes the PC panel invalid? Guess not, though unrespectful toward the boats, than cannot have the possibility to check any undeclared COI, or the feeling that a certain Judge or panel could not have the expertise necessary for the level of the event.
Still, parties have the possibility to make their says before the hearing starts. At least. Better than nothing.

Publishing Appointment of Obsevers as per P1.1
The appointment  by PC as per P1.1 is a due act of PC. Without nomination,  persons on the water have no right to apply P 1.2 (the "may" in P1.1 means PC may also not appoint Obsevers, if PC deems Appendix P unapplicable due to local situation)
Also, aggravating circumstance,  with P1.2 there's no exchange of points of view, no discussion: a yellow flag is for life. One reason more for boats to know who's who.

So, i believe that the Observer's appointment should be published, to confirm to the world that PC  complied with P1.1,  that the person on the water are empowered to act as per P1.2, and to give the possibility to the boats to check themselves any COI, or to express their personal opinion about the nominated Observer to PC, before going into the water, and before it's too late.

By not publishing the Appointments on the official board makes the Appointments invalid? 
Big question. 
For me, it's definively unrespectful toward the boats. So much paper published, and not make them knowing who can affect their race?
Resuming:  being the Appointment as per P1.1 a due act of PC, and being the application of Appendix P an act that governs the event, and rather heavvly, and being the fact that person not appointed cannot act as per P1.2, the pubblication on the official board of the Appointments is a must;  and by not publishing it,  might we enter in the area of improper omission of the PC (62.1 a),  with the relevant right of redress for the yellowed boats ? 

Myself, i publish it;  out of  respect to the boats, but also not to be caught in a request of redress, difficult to handle.

Aldo, using the Appx P Observers as an example, you make good points of why someone might choose to be more formal in their process, documentation and publication/notice of appointments and why that might benefit competitors. 

That said, to request redress a party would have to convince a PC that these appointments were an “improper action or omission” due to lack of process, documentation or notice.  

I do not see in your post where you support that conclusion in the RRS. 

Welll, my common sense.
From Collis Dictionary: "" If you appoint someone to a job or official position, you formally choose them for it."" The word  "formally" makes a difference.
I never saw a Board of Directors being appointed, without a written, signed, and published document. Neither a balance sheet, or the appointment of a new Government, or the President, or any Executive Commitee, etc.
No ""formal appointment" that came to my mind could be only verbal, or maybe in written form, but anyway not made aware to the ones that have any relation to the appointment.
The PC has to be "appointed" (89.2 c), the Observers has to be "appointed" (P1.1).
Not publishing the appointment it means not respecting the formality of the appointment. (to formalize, Collis dictionary:  If you formalize a plan, idea, arrangement, or system, you make it formal and official). 
No formalization, no officiality.
And for that, I can understand if someone (and that's me) can take the appointment as irregular.

Aldo, Ok … what about the RC member on the signal boat that is calling the start/finish line … and maybe add to that the pin-end boat doing the same from a position outside the pin?  Do we also have to post their appointments also?

RC also has to be "appointed" (89.2 c).
And ""any other person or committee performing a race committee function"" is RC (RRS, Introduction, terminology) 
Yes, Angelo, i deem those persons you mentioned are  RC members, and their names should be posted.

Aldo, though you make good and reasonable arguments why these extra steps are a good thing to do, absent “documents that govern the event” that require them (such as Conditions, Regs, CR, NoR), I’m not convinced that not doing so, alone, constitutes an “improper action or omission” on the part of the OA, RC or PC. 

Angelo,   i'm not also definitively convincent myself about the simple fact of not posting being an  "improper action"; I argumented the "might", Devil's advocate points, but might not.  Or there might be conditions where it might 
Generally speaking, any action made from a person not empowered for that action, might well be an improper action.
So i got a yellow flag, or a UFD, or NSC. OK. Who give it to me? Was he empower to do it ? From what? Show me.  it's a mine field.
RC and PC nominations are always posted. If that is a must, why Observer nomination should be different? 
Anyway, my main point:  why taking the risk? 

and thinking it over again, back to your original question, yes, i think that a non - wirtten and not-bublished appointment can make it invalid. Well, upto when all goes straight and fair, ok, but at the first occasion of dispute, the "appointment" is questionable.
Question 2: not specifically written in the RRS, but see the wording in Terminolngy ""Other words and terms are used in the sense ordinarily understood in nautical or general use"". And I posted the Collis Dict. about the formality of an appointment.
Yes, i do deem them invalidable.

I have deleted my post and will not be commenting on here further

As soon as we have the word improper in there aren't we immediately talking about redress? As for an invalid appointment, I'm not sure the concept exists in the rules. So for what little it's worth my opinion is we are searching for something that isn't there. Appointments may certainly be unwise, but I can't see that makes the appointment invalid or improper, although it may mean that a PC may decide to put little or no weight on their evidence in a hearing.

 If an incompetent 'judge' is appointed to enforce RRS42 who has no knowledge of the rule the appointment is unwise, but I don't see a rule that makes it invalid or improper unless there are event requirements as per Angelo's 22-Nov-01 15:49 . But contrariwise an individual competitor is certainly entitled to redress if the incompetent judge wrongly penalises them. But the redress is for the action, not the appointment. I submit incompetence is not improper or invalid. At a club level I may have assistant race officers whose only knowledge of the rule book is that there must be one, but if their only duty is to pull on halyards when asked its not an issue. However if they were called as witnesses for an incident the PC might discount their evidence. 

So I submit the answer is as Angelo's PS in 22-Nov-01 15:49. 

me too i'm not going further. I expressed my point of view, if you do not share it, well, it's your right.

Angelo Guarino

Said Created: 22-Nov-01 15:49 

 Nothing in the RRS says appointments shall be in writing or shall be communicated to competitors.

Conceivably one member of a race committee could 'appoint' a person to a protest committee or a technical committee, and the majority of the committee might say 'we do not agree with that appointment, and it is not a proper appointment.