Merge Sample Var with Population Var

Hello, i need help. I have 4 variables i.e.
VRegS VRegP VregPmake and VRegSmake.
Capital S stands for sample while P stands for population

VRegS=vehicle registration for sample

VRegP= vehicle registration for population

VregPmake=...make of a vehicle from the population

VRegSmake=...make of a vehicle from sample
Sample size is 100
Population is 1000

So, I have 100 observations VRegS, 1000 observations of VRegP, and 1000 observations VRegPmake.

And
100 missing values of VRegSmake

So, I want to replace VRegSmake
How?

Here is the catch:
The 100 makes for S can be found in the 1000 makes for P.

I can't use

. replace VRegSmake = VRegPmake if VRegS == VRegP

Because S is smaller than P and the values are not matched one to one, even if I sort, you getting the point?

So, what should I do?