Exchange 5.5 personal contacts

I am running Exchange 5.5 SP4 on NT 4.0 SP5. Outlook 2000 as the desktop client. My CEO’s contacts have 542 entries. There are individual and personal DL’s in there. Twice now when she has gone in some of her DL’s and personal items are missing. One of the DL’s had been in there for two years, one individual was there for 6 months. She had been using a palm pilot with intellisync. She has not used the palm or done a hot sync in over a month.
We do not use personal PST’s here, that function has been disabled. No one would have deleted the items that are missing. Does anyone have any ideas on how these items are disappearing?