Just a few weeks ago, I struggled through three days and 6 brutally hard games , 30+ hours struggling at a board, traveled overall 400+ miles, spent hundreds of dollars in food, entry, and gas. Suffered through the agony of defeat, won not a single dollar, trophy or even congratulations all of it to win 1 single rating point to go from 1928 to 1929 at the 2008 Texas state championship!! Thank you, thank you for fixing my 6 rating points three years ago(though i had to pull teeth to get them) but thank you!!
Most changes that arise during rerates are because of newly rated events that were rated out of chronological order or data corrections, such as changing a L to a W or changing the USCF ID of some player. For unrated players two other types of data changes are changing the player’s birthdate (which affects the initial estimate for an unrated player who is under 26) or adding the FIDE ID of a FIDE-rated player.
For players who have been inactive for many years, sometimes when they return to rated play they are mistakenly treated as unrated again, and we have to reinstate their former USCF rating manually.
Changing the information for just one player can have a ripple effect on all of that player’s opponents, then for some of the opponents of those player, etc., in that event and then in subsequent events.
The classic example, one that actually occurred some years ago, was that the ID of a master in NJ was used by mistake for a scholastic event in California due to a transposition of two digits in the ID. Not only did the master take a bit hit but several of the kids why ‘played’ him had large ratings increases.