A start line is a start line as defined by the race documents including extension - but normally just defined as a start line. In normal fleet racing the boat is X-Flag if you are over the start line at the start (0 seconds). If you are above the start line at the start and haven't crossed it, even sailing above, the boat is DNS not OCS and therefore can't be 'recalled individually' so no X-Flag can be used. The boats that started normally for that match should have continued racing regardless. This also the normal situation in Team Racing. Assuming this is a P flag type start so none of RRS 30 comes into play at all. Personally, I would have left the race running (no recall, as it doesn't apply) and told the scorer/scribe/finish boat about the 2 boats being DNS  (if they never come back and start within start time limit (if stated) ) - it wasn't RO error, it's the boats' error for not crossing the start line as defined by the race documents. Also depends on the age and experience - if it was more of a learning environment, I may do something different.

You've stated this is team racing and then brought up Match Racing - two different Appendices (D & C respectively). In Match Racing if OCS at start or failing to enter start box on time is a penalty to that boat (or both, then they cancel out) - Code Flags for recall are not used in Match Racing generally.

Nicole re: “If you are above the start line at the start and haven't crossed it, even sailing above, the boat is DNS not OCS and therefore can't be 'recalled individually' so no X-Flag can be used. ”

I don't think that’s precisely correct.  OCS includes “did not start”. 

From Appx A10

We have an old thread someplace where we dove into this question.  Lemme see if I can dig it up (or anyone else who finds it please post). 

The “shall” RC instruction for the X-flag is described in rule 29.1.  It does not include any statement regarding the boat crossing the line. 

Rule 29.1 uses "starting line" and "starting line or one of its extensions" separately and specifically, suggesting to me that there's a distinction. Use of "starting line or one of its extensions" in C3.2(a)(1) (changing 29.1 for match racing) reinforces this impression.

So in fleet racing (or team racing, which doesn't appear to change 29.1) I don't think a boat that's on the course side of an extension of the line at her starting signal has broken 29.1. Obviously such a boat would still have to get below the line to start properly and would still be keep clear under 21.1 while doing so. Sounds like displaying the X flag in this circumstance was an improper action by the RC.

Was the redress request deemed not valid because there was no improper action or omission, or for some other reason?

Assuming that RRS 30.1 didn't apply, the race committee made two errors regarding RRS 29.1 

Tim, but even as you describe, a boat could be on the course side of the starting line without crossing it in close proximity of their starting signal.  Crossing the line is not a requirement. 

I found the thread.  It was my old “puzzler word-problem for NYE”.   It’s a very long thread with lots of diagrams   and of course head-of-pin-dancing. 

https://www.racingrulesofsailing.org/posts/501-ocs-around-the-pin-end

Here is probably the most focused pic on the question from my puzzler thread …

Gun goes off at #2, no X-flag?

Thanks for your answers!

Tim, not valid due to SI procedure.
Peter, RC signalled promptly after the start. 

Another comment: If the extension IS in play it will be much harder to observe boats returning at the starting vessel end. 
In this specific case PRO said it was hard to determine from the starting vessel end  if the boats were positioned outside or inside at the pin end. Much more so if it´s a longer line with greater number of boats.  In this race it was eight boats. 

I will check the thread! 

Ahh yes a lot of beautiful "boxes" in the thread. Thanks! Hard to apply without being defined I would say. Laylines after upwind start must be included anyway as well as all angels in other starts. 
I believe that RC has a grade of freedom here... and that it´s hard to get redress ("no fault of her own" and "omission by RC"). We have to wait for the jury to decide...

If I'm a judge in a hearing, I could probably be convinced that the conditions of 29.1 were not met so failure to display an X flag is not an omission.

If I'm the PRO, X flag almost certainly would go up, I would think.

In either case the boat has not started properly and has no excuse for not knowing it, so score OCS.

This is the harder one from the old thread, I think. If the starting signal is at 2 (and assuming the bow is on but not over the starting line) has she complied with the definition of start?

I suspect this is another one where the boat is technically wrong but no race officer would ever spot it or call it.

Hi Tim
I disagree on orange boat not starting correct.

Tim, the reaching start is a good one too …

Anders, it’s based on the perpendicular projected area concept of the pre-start and course-side of the line not including the extensions. 

The green line is the boundary on the prestart side between the starting-line and it’s extension.