Use by dates and leftovers

[Figure17a]

I have a large gammon joint I forgot to cook. If I cook it on it's use by date, do I still get 3 days for the leftovers?

In reality, if it looks and smells ok I'll use it, but I wondered what the official answer is?

Yes because it is now in a cooked state

Or you could put it in the freezer now while it's still ok and you'll be fine to defrost & cook later on