I agree with you Squire that they flew what they could. What I was aiming at was how successful the P-39 was in their hands and the main ride for quite a few of their top aces. Was it all before 1944, or did the P-39 continue to be a top fighter into 1944-45 and against the later 109/190 models? I apologize for my ignorance but I know very little of the breakdown of kills into years and models in the VVS.
Usually, when more advanced fighter are available, they tend to take the leading role and inferior models are still being used but moved to secondary roles, or less "busy" regions. This is in particular true in the pure fighters roles where there is much less compromise than in attack, recon and training. The top pilots normally transition into the more advanced fighters, though not all of them of course. Yet in the Russian case, many stayed with the P-39 (again no hard data, just anecdotes and impression). Don't be afraid to tell me I am wrong - I really want to know.
How did it look from the LW perspective? Did German pilots in the eastern front respect the P-39? Perhaps someone that read more LW memoirs than I did can tell.