What blood types are possible among the offspring of a couple of blood types ab and a?

If you were to make a punnet square you could put the blood type AB on top (or AA) and put the blood type AA (or AB) on the side. Next add the blood types together. You would 50% blood type AB and 50% blood type AA (or blood type A) which means only AB and A are possible. If you need to know about AO then comment.

No they’ve not done that