There is no difference.  P38 is the least correct, but most commonly
used designation.

The RR model you are referring to was actually originally coded the
"38A" by LR, but for some reason it was prefixed with a P later on by
someone unknown (theorised that it was a shortening of Project 38A) and
'P38' seemed to come into general use, but some people also refer to it
as the P38A.

There were revisions to the RR at the time around your friends model
year, perhaps that is why there is some confusion.  Best to work from
the VIN if there is any doubt.

Matt