Standardized unit values

[Bioman]

I was under the impression that with the McNamara unit values all units of the same type i.e. T34 would be the same. I found that the T34's in the alt scenarios for Moscow '41 are rated at values of 17 and 19 but the same units in Moscow '42 are 13 and 19.  In Kharkov 43 they are 19 and 20. In Korsun '44 the T34/76c is 14 and 20.  In Stalingrad '42 the T34/76c is 17 and 19. I realize that the T34/76c units are a variant of the other listed T34's so the values could be different. I just don't understand how the values for the same listed tank are different in the other 3 games.