That isn’t really correct. Leopard 2AV led to the Leopard 2A0 (after being slightly redesigned to address the lacking protection).
While AV indeed stands for Austere Version, that’s in comparison to the original project which called for;
CITV
RCWS
APU
And a few more gadgets. All of them were ereased from the requirements due to costs, hence “AV”. Trials in the US played a secondary role in all of this.
Yep, its PT20/T21
The PT19/T19 had the same FCS and welded over thermal slot, afaik it also got the 120mm later on
The third AV, PT20/T20 used the EMES-13 as on the PT.16/T.14(mod)
It is correct that T19, T20 and T21 didn’t receive a thermal imager. However, it is quite likely that one of these was used to test the Common Modules thermal imager and german thermal imager. All 3 turrets were also able to be retrofitted with a thermal sight.