BelOMO Zenit-E serial #s

A friend just gave me a BelOMO Zenit-E as a present and it has a really odd serial # I have never seen before, it has couple of extra numbers in it than it's supposed to for that year. Anyone seen anything like that before? Serial # is 81020355223.

Thanks,
Vlad

Very interesting Vlad, I have also never seen it before.
My speculation were, that the s/n has 7 digits as usual, but the first 4 digits are year + month,
in this case camera with s/n 0355223 from Feb.1981.

BUT it is only my speculation.

Regards, Alexander

It's an interesting theory, I just never seen this kind of convention of Soviet stuff before... thanks Alexander.. another mystery on our hands