When is Set Over? Too Late to Correct Error?

[timasdf]

When serving team has appears to have 24 points, R2 checks with scorekeeper, then gives set point signal. Serving team gets the point. R1 signals end of set. Shortly after teams have changed courts, the scorekeeper determines that something was incorrect. R2 confirms that the serving team...

A. ...actually has only 24 points.
-OR-
B. ...had an incorrect server for the would-be 25th point.

At what point is it too late to fix? Despite multiple text searches of my digital copies of the rule book / case book / manual, I was unable to find anything specifically referencing this. Rule 1-5 is super generic. No Case Book references for Rule 1-5, either.

Thoughts? Rule References?