Here's another thread with a bunch of info:
http://www.project1999.com/forums/sh...d.php?t=206539
main resource:
http://www.angelfire.com/freak/eqjon.../tofs/tofs.htm
Basically there is strong evidence
for (in our timeline):
1) The mirror room on 7 being able to port you to any level, if you have the correct key
There is strong evidence
against (in our timeline):
2) Higher level keys make lower level keys useless, so you could use key 5 to click though floors 1-4.
There is mild evidence
for and against (identify description, peoples memories vs not being explicitly mentioned in the angelfire guide page):
3) Tserrina's key is a master key that will allow you to click any floor from the mirror room on 7.
At some point between Velious release and the time that /keychain was added 2) became true. I'm guessing it coincided with /keychain, as adding the 5th floor key to your keychain would add floors 1-4 as well to your keychain.
At some point after Nov 2002, 1) became false and all the mirrors in the mirror room would only port you out to Iceclad.