Your top picture is one of the prototypes, so no AAMG.
The other two pictures are museum pieces. No AAMG's on them as they are museum pieces.
Just so we get this correct, because you have a point, the initial T-64 produced in 1961-66 was based on Obiekt 432 with a 115mm main gun and no AAMG. About 600 of these were produced, but they were only considered in limited production, mainly to work out the bugs in production. In 1967 serial production of the T-64A, based on Obiekt 434 with the 125mm main gun, started. In 1979-81 ALL T-64's, regardless of production time, were rebuilt to T-64A specifications which included adding the AAMG to the initial T-64 batch, as well as unifying the storage design on the fenders, among other things. I am not sure how many 115mm armed T-64 were rebuilt and how many scrapped at this point but enough were rebuilt that they were renamed T-64R to differentiate them from the 125mm armed versions. As the initial batch of T-64's came up for need of overhaul after 1981, they were retired, as their need for 115mm ammo complicated the supply system for T-64 units.
And that is why the 115mm armed T-64 can have, and not have, an AAMG. However, I was not thinking about the 115mm version as I am not sure how much use it got in field as the initial production T-64's were very unreliable.