You dont need an ATPL to act as commander of a single crew type even if its operated multi crew under an AOC. So your company can promote you to captain without faffing around with foreign licences. You upgrade to an ATPL when you do a multi crew type rating by asking the examiner to give you an ATPL skills test. If you were building hours in a single crew aeroplane flown multi crew under SOP's agreed with the CAA or under an AOC those hours will count towards the required 500 for the issue of an ATPL.
Hope thats helpful