[Jens]

IIRC there were at least 40 changes between La-5FN and La-7. But i think it's right to say that in Germany this would be a letter behind the type designation.

Bad quality of parts shouldn't get to the assumption, the soviet planes hadn't good aerodynamics. In german reports about captived planes is stated, that british and soviet planes had in general worse quality in production, but this cannot be said about aerodynamic parts. Such differences were one of the reasons for the higher production figures of the allied industries. (Source: Budraß)