If it is an issue, I would call your provider and ask them to check the number. I doubt your pbx will cache the number without the option being enabled.. I know CID Superfecta can cache results, hence the question.
It would seem the trunk provider is providing you bad data, they are the ones that pass the CID info onto you, but I really do not know the ins and outs of the way it works.
I use Sipstation for my trunks, CID has always been good, but if missing I use CID Superfecta to do the leg work.