Well, the most reasonable solution i could think of is:
Yugoslavia produced its own ammo, and the Croatians and Bosnians most likely did not buy any new ammo for their tanks. They used the ones from captured Yugoslav barracks (See
Battle of the Barracks) now, what kind of ammo Yugoslavia used, i don't know, but it surely was very similar to the Soviet, although which of those was better is questionable. It is possible that YU didn't exactly copy the soviet ammo, they were more prone to produce modified versions of soviet technology. (Just like the M-84 isn't an exact copy of the T-72, but a slightly improved one due to later introduction than the T-72, when new technologies were available)