[PMoz99]

I've attached the kill list for Reznak as it appears in Osprey's Slovak Aces book.
In the same book it says that 13.(slow)/JG52 returned its remaining 6 109F's on 5 March in exchange for 9 109G-2s. The G-2s were exchanged for G-4s by the end of the same month.
That suggests Reznak's first 3 kills were in an F, the remainder in a G.

As far as I can see, Osprey's Croat Aces book doesn't provide any insight into Boskic and Starc.
It says Boskic claimed all his kills in his first tour, which it would seem ended in October 1942. CdeGloire has his first kill in an E, but only lists 4 of his 8-13 kills (depending on whose list you prefer).
Osprey also says Starc reached 9 kills + 3 unconfirmed (2 were later confirmed) by October 1942. CdeGloire lists his first kill as being in an E, and the rest of his 10-11 kills, starting from 9/10 July (!!), in Gs.
According to the unit lists at ww2.dk, 15.(kroat)/JG52 received its first Gs in July 1942, but from the info there it would appear it was not until on or after 26 July ..........

Cheers
Peter