[PN79]

Hi JaM
You are right. Czechoslovakia produced 3 variants of T-72. Basic T-72 with 2A46 gun with 39 ammo, laser RF and without sideskirts and smokegrenade launchers. This variant was in service since 1981.
Then was produced T-72M with same armor as T-72 but with 44 ammo for gun, sideskirts and smokegrenade launchers. I don't know when this variant was fielded. Technical documentation come to Czechoslovakia at the end of year 1981.
The last version was T-72M1 with same FCS. Main difference is only in armor (front hull and new turret).

T-72M4 is modernisation of T-72M1 so basic armor should be same.
Regards