If you are looking at the VIN on the ownership documents it may have been assigned by the DoT for the state/province where it was first registered. If there is a VW chassis then you find the original VIN on the tunnel between the seats in front of the inspection plate. See this link for decoding the VIN https://www.thesamba.com/vw/archives/info/bugchassisdating.php
If it has 1981 and MiGi it sounds like you’re looking at the kit serial number. I think that’s irrelevant to your registration unless the car’s never been registered before by a state motor vehicle department.