Perhaps some of the Pre-production A4KT boards had barrel type batteries. Otherwise & afaik, 4000T's were Always a Coin Battery. I've owned several myself & have seen loads of others too, but all with Coin Battery.
RE the A4KD Rev D with on board CPU & Coin Battery, these machines were a vain effort to reduce costs & the battery in there was a cheaper solution than the barrel kind because of the surface mount process making the whole production cheaper.
I guess the A4KD rev D just rolled on with progress, as it did with the Coin Battery from the A4KT. ;-)
