Anything that changes the meaning: a wrong star count, a wrong date, a wrong licence, a feature credited to the wrong project, or a claim the sources do not support. Those get a dated line saying what changed.
A star count that has moved since the snapshot date is not a correction. It is a snapshot, labelled with the day it was taken, and it is expected to age.
Typos and phrasing that do not change the meaning are fixed without a log entry, because logging them would bury the corrections that matter.