Thanks for the info DGM. In the mean time I have found some more info at
http://www.sas1946.com/main/index.php/topic,14631.0.html This Karabas Barabas knows quite a lot about Yaks.
He writes:
Yak-7 without razorback more than 4000 from all 6400 Jak-7 (Jak-7UTI and Jak-7V, Jak-7, Jak-7A, Jak-7B)
5120 Jak-7 with M-105PF
Jak-7 43 (~25-3x series Novosibirsk plant N 153 and ~10 series Moskow plant N 82), max speed 514 +-2-3 km/h - 570 km/h
Jak-7 autumn 43-44 (~40-50 series plant N 153 and ~20 series plant N 82), max speed 531 +- 2-3 km/h - 580 km/h
I read this as Jak-7 43, highbacked version and Yak-7 autumn 43-44, bubbletop version, series 40 - 50 for Zavod 153 and from 20 serie in Zavod 82. That would give a date of September / October 1943. Can someone confirm this.