Hi Neil,
If the commanders cupola has a split 2 piece hatch, or the turret does not have the small bulge on the front lower left side, it would indicate pre 45 production. The addition of the bulge and the single piece hatch were late 44 early 45 additions. The Czech produced T34s had the turret roof ventillators at the rear of the turret until production ended in 1964. The Russians split the vents fore and aft in 1947. Looking at the neatness of the turret casting, I would guess post war Czech production.
Perry