[Fred Nerks]

...And there were things like scratches disappearing over time - which would indicate that scratched microfilms had later been replaced by more pristine ones.

Even my normal good sense of humour is deserting me, last question:

Did the scratched and the non-scratched materials contain the same information?

[butterdezillion]

Yes, they contained the same information.

But the scratches disappearing over time showed that the microfilms had been replaced, which makes no sense to do since the information was the same on both - unless the replacement with the “cleaner” microfilm was to cover up mistakes made when the previous microfilm change-out had been done.

IOW, the obvious manipulation/changing of the microfilms makes all versions of them suspect - because you only go to the trouble of changing out a microfilm roll if you think there’s a good reason to do so.