Science says when its frozen, it is SAFE indefinitely and only quality issue may arise. This is known to all of us - QA practitioners. And we can be practical in all sense of the world and may allow the use of this out of shelf life ham because it is frozen anyway.
However, just to give you some perspective on a worst case scenario:
If god forbid, there was a food poisoning incident and the source of illness is your product that uses the HAM as one of its ingredient. During investigation by you and your country's regulatory agency, it was found (the regulatory agency discovered based on your record trail) that the ham used to make this product was already out of shelf life, and then now your regulatory agency is already incriminating that the source of the illness is the out of shelf life ham or simply let's assume after all the info is collected and investigated the actual source of illness is the ham.
How are you going to justify this to your regulatory? How are you going to justify this with the people who got sick? Technically, you cannot go after your supplier of ham because they indicated the shelf life of product at 3 months and then you decided to store it in freezer and extend the shelf life.
My point is, logical and practicality comes with our job - but it is important to cover you a** very well. Maybe ask the supplier for a shelf life extension, or for a specification which says that if the product is kept frozen, then the shelf life is 1 year. Or if this is a recurring issue, you can even make your own shelf life study for the frozen ham to see how's the microbial load by 6 mos, 1 year etc.
Apologies as shelf life issues is very close to my heart as this is one of my hard limits in my QA job.