[morzh]

>>All other paper caps measure fine, most display more capacity as they should, like 30nF instead of 10nF.

That does not make sense.
To measure fine, a cap should be within tolerance; it does not work as "the more the better".

The best thing you could do is replacing all paper caps and not trying to separate good from bad: there are no good ones there. Good paper caps from that era simply do not exist. Or, if they do, it is considered a miracle and such a cap would be displayed in a local place of worship for people to marvel at.