When you created the worker account, did you fill in fields manually, or did you ask Helpdesk to synchronize the account against a contact in the domain?
o Enter new values
o Use this contact: Bolster, Joe J (NT ID = domain\JBolster, E-mail = jbolster@domain.com)
I would say that the ones that stuck did not pull information from your old domain (Option 1), and the ones that are returning were set up to pull information from your old domain (Option 2) and therefore continue to do so.
I would create new workers.