Just had an idea which might work ... if ...
Is your 3.7.x a clone of your 3.6.x? If so, the passwords don't change on clones/upgrades so am guessing you could copy the text you see in the password column of the 3.6.x and paste it into the password column of a user id 1 guest account.
Even if that didn't work ... no harm done ... cept your still stuck with the issue.
But if it did ... that would save a lot of time and work!
Fingers crossed!
'SoS', Ken