An official rating list is a snapshot of the ratings information we have on players as of a particular point in time, currently around 11:45 PM on the third Wednesday of the month before a new ratings list becomes official.
However, the post-event rating from your most recent event at that time can change later on, due to rerates.
For example, suppose you played on a tournament on the 10th of the month and that was your most recent event in our records as of the time the new rating list was created. Your post-event rating from that event would become your new published rating.
However, suppose you also played in a tournament a few days earlier but it had not yet been received and rated by US Chess by the time we generated the next official ratings list. Once that event is received and rated, it needs to be sorted into the proper chronological order, which happens during the next rerate. When that occurs, both your pre-event rating and post-event for the event on the 10th may change.
Similarly, suppose there is a correction made to the event on the 10th after the new ratings list is prepared, such as an incorrectly reported result for one of your games. When that correction is made, your post-event rating from that event is likely to change when that event is re-rated.
In either case, we do not go back and revise the published ratings list.