Last night I logged in with an account that has a 20 character password. Or so I thought.
The Cool VL Viewer warned me that a password could not contain more than 16 characters.
So I tried the LL viewer and FS, and I could "just login".
Then I tried again with The Cool VL Viewer but deleted the last 4 characters.
Et voilà... I was logged in.
Apparently some other viewers just drop the superfluous characters silently(!)
Even Linden Lab's password change form didn't warn me when I made the passwords longer last time.
I just realised the description of the password change field says it should be 6-16 characters long, but when I paste a 20 character password it just says "Best" and saves it.
Thanks for the warning
My passwords can be less safe than I wanted.
(I will put in a support ticket with Linden Lab).