If a level gets backroute-fixed so an old record (e.g. fewest builders) is no longer possible, NL still displays the old record.

However, we wouldn't want records always to be thrown out with every level update, because some updates are purely cosmetic and don't affect results.

My suggestion is that the Advanced Options tag should contain a "Reset records" button that resets records for the currently selected level, or, if a rank is selected, every level in the rank.

Agree, this is a good idea. Have noted this to include for V12.10.1, as it should be trivial enough to include in a minor update.