There is no difference, 1937-62 are all the same.
GM changes part numbers for no apparent reason.
My 1961 parts book is back to the 838869 number.
One possible reason for a part number change is the cover comes with a seal. I think the early seal is leather and at some point it was changed to some kind of rubber. That kind of change will cause GM to issue a new number even if the part interchanges. Still I can't say why they went back to the original number in the later parts books.
