Why does Font Book font count vary from account to account?

Here's the situation.....

I'm running OS X 10.4.1 on the most recent model of an 17" AlBook.

I have six accounts, one administrator and five user.

The entirety of my font collection is contained within two folders and should
be accessible from all accounts.

System/Library/Fonts

Library/Fonts

There are no fonts installed that are visible only to a single account.

What I don't understand is that if I open Font Book when signed on to the
different accounts the displayed font count, the one shown at the bottom of
the Font Book window, varies, the count being either 201, 212, or 213.
According to my own calculations that number should be 213 for each and every
account. The 213 is what I see in the administrative account and in one of
the user accounts. The 201 is for one of the user accounts, and the 212 for
the remaining three user accounts. About 90 percent of my connection time is
in just one of the user accounts, and that one reports 212 as the font count.
These counts remain consistent from session to session and through shutdowns.

Any ideas/answers/suggestions?

Many thanks in advance.