Peter .. I don't think I've ever used the very popular response before on the forum .. but here it goes.

"It depends" (man .. that feels good .. I can see why it's so popular! LOL). 

Before the more recent updates to Appx J, there was much more overlap (and inconsistency) between what was in the NOR and what is in the SI.  Nowadays, the NOR is more about 'information that a boat would need to know before deciding to enter or prepare for the event' and the SI's are more 'information that a boat would need to know to race in the event'.  Obviously there is a lot of overlap there, but if you take any piece of info that would feed into the decision to enter or preparation/crew/logistics/possession-of-equipment, then that should be in the NOR.

Given that "it depends" what comes next is going to be in the eye of the PC if someone thought the notice for the change was not adequate for that specific change. 

For instance, if crew weight limits are going to be enforced, a boat would need to know about that well in advance so that they can assemble a weight-compliant crew that are available.  That type of change would need to be made many weeks in advance IMO.  On the other hand, in a 3 day event the first 2 days were a wash-out and the OA/RC wants to start at 1000hrs instead of 1100 hrs on the last day to try to get in at least 3 races, posting the change to the ONB the previous afternoon (maybe giving the heads-up along with the Day-2 abandonment that this is a possibility ... and to watch the ONB) would likely be seen as adequate notice.  On the contrary, extending the last-day's racing cut-off time the afternoon before could be seen as inadequate as some boats might have flights and other logistics/obligations which would force them to miss the later racing.

To your specific example, I'm having a hard time understanding how a late NOR change can alter the handicap system into which a boat is entered.  When you enter a race, you enter your boat in a class (either OD or handicap).  The handicap system is part of your entry. If you are racing under PHRF, that's how you enter.  If ORC/IRC, that's how you enter.

Within handicap systems, there are variables that are build into those systems to account for different race-course configurations and sometimes racing conditions.  For instance, PHRF has different ratings for random-leg courses and W/L courses .. and other handicap systems have different ratings based on wind/sea conditions.  The discretion on those variables is typically build into handicap system itself as part of that system's Class Rules, handing that decision to the RC to choose as best they can which rating-subset apply to each race.   I have heard RC's make an announcement 5 min's prior to the start of each race which band of ratings the race falls within (for IRC).  But I don't think that's changing the "handicap system" but rather the rating band within a system based on the race and conditions.

Also, in PHRF there is Time-on time and Time-on-distance calculations.  I would think that would need to be stated prior to starting the race.  As a judge looking at a request for redress I would ask the requester, "Would this information have made a difference in your preparation for the race, your decision to race or how you conducted yourself in the race?"  On first glance, being rated ToT vs ToD would seem to make little/no difference to those questions, but I would want to consider the answer/explanation given.

Does that help?

Angelo & Peter,

As someone who has fought hard to track down all the holes in the leaky caldron of some NoRs, I have an addition to what's stated above:

Often the NoR for a significant regatta is published a year or more in advance. This is particularly true of significant races across oceans or massive events where dozens or even hundreds of competitors are expected, and especially for events where owners are considering designing and building a boat that conforms to the exact information in the NoR and, more importantly, the the exact information in the various Rules that are cited or implied in the NoR. For these regattas, the NoR publication can end up serving as the defining document for a large number of things that are buried in other documents whose revisions are made more often than the time between the publication of the NoR and the start of the first race.

The obvious ones include:

There are more, but this illustrates the point. My suggestion is that in all NoRs, the complete title of the document being used, its publication date, and any modification tracking provided be cited in the NoR. Thus (as of this writing):

It can be very onerous to tease out which version of these rules are applicable and which will be made obsolete in the time between the publication of the NoR for a race and the start of the 1st race. Indeed, I've had a fleet hold a meeting at their National Championship and attempt to change the Class Rules to outlaw an innovation that was not predicted by any of the rules. Ever since, the exact version, date of publication, and term of any rules mentioned in the NoR has been appended to the bottom of the NoR and carefully footnoted where first used.

Similarly, I know of one large yacht that was cut in half to modify its length substantially based on the initial NoR for the race and an obvious error in the handicap rule. The owner and his team informed the OA and the Rule vendor of the obvious error in writing and by phone. They were ignored. The error was rediscovered much later by the Rule vendor, and then the OA decided to change the Rule. Given the owner's investment was already well over $2m, lawsuits were threatened, the OA backed off, and the heavily modified boat was allowed to race. Not the outcome anyone wanted.

As a dear friend of mine likes to say: "The starting gun is when the NoR is published. More races are lost by not reading the NoR and Sailing instructions than any other cause."