As software is updated with Git, the specific changes are highlighted. This means you can verify the code one day in its entirety, and as the software is upgraded, would only need to review the specific changes as opposed to reviewing the entire code again.
that is only possible and easy when you check each commit every day individually. but if you are checking the difference from version to version (for example from bitcoin core version 0.19 to 0.20) then there is going to be a large number of commits with a huge amount of code changed, added or removed which makes it extremely difficult.
in core's example there was 2033 commits, 1254 files changed with 78,888 additions and 72,492 deletions.
https://github.com/bitcoin/bitcoin/compare/v0.19.2...v0.20.0