Expired Userid's

Setup a thirty user accounts, all in different times. I just found out that
fifty percent of the account expired at the same time. What is perplexing is
that most of the expired accounts were configured, where the passwords never
to expire.

I checked the event logs and found nothing out of the ordinary. Anyone else
experience this or can tell me why this happened so I do not repeat this in
the future. Thank you.

SM