Yes, you can determine the firmware of the PSP by looking for a specific character on the box:
no letter = 1.5 (North-American release)
A = 1.5
B = 1.51
C = 1.52
D = 1.52
E = 1.52
F = 2.0
G = 2.01
H = 2.50
Here is a picture of were to look for the character on the PSP box:
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