I think there was a change in search that showed up at some point to allow for searching a different way around, by email or number or something that didn't work with UDS well before.
If you're referring to directory data, that is whatever is configured in the associated end user record, not whatever you've configured for the user's extension.
If you have synchronized in User A, with a telephone number of 12345, and assigned them internal extension 12345, searching for User A shows their business telephone number as 12345. If User A retires or leaves, and you do not remove this account from the system, but instead provision User B with 12345 and same internal extension, then calls from 12345 _may_ display User A as the caller ID data, based on how UDS lookups are done for a contact instead of respecting the data sent with the call in SIP signaling.
I suppose there is another possibility, and TAC can confirm which is doing what here, but it is possible that your clients are listening to data retrieved from Outlook and compositing the user's contact in a manner not suitable to you. This has caused me some trouble in the past, but I don't recall if the contact source is noted in the Jabber logging to be sure that's where it came from.
Those are the only two things I can think of which would impact more than one user at once. I haven't updated to 12.9.2 yet, but maybe I will if it fixes some of the contact resolution problems I had been having.
