Firefox has a password reset sent to the email registered Firefox account that is different from Thunderbird. Thunderbird connect to the actual email server itself - TB by itself can't do anything unless it connects to the email server. So not sure why a update should stop the email TB from working. Are you not able to go directly to the email server that TB connects to login? That is where the login should be verified and if it doesn't work then he needs to contact that email server support to resolved the login issue.

Version 72 was years ago and there was never a public release of it.

would I be correct in assuming the update was to 102.14.0

Why do you say it has "made Dad's T-Bird password unusable" unusable how? Did the application update and that was followed with connection errors relating to an inability to connect and a generic message about passwords? If that is the case the issue is almost certainly in security software external to Thunderbird. The antivirus/ software firewall is generally the issue post update, not recognizing the new version number. Correct that and everything works again.

I have an old password on in a text file for Mozilla but until the last t-bird update (v.115.2.0) it was never needed. Now t-bird won't recognize it or load without it, nor does my gmail password work. There is no option to change it without having the old password accepted first--classic Catch 22.

No reply I've seen provides a workaround for this consistent with the internal menu options.

I was able to log in to the Mozilla website with whatever password is hidden in t-bird's now-inaccessible password file, but I cannot retrieve it to download mail. I can still access my gmail account via Firefox, but Google's site is horrifically inferior to the t-bird format.