That's a good question, that I don't think anybody knows for sure.
Supposedly, the 1937 model came with the reflector provision, and the 1938 model came without it, because that what these two advertisments show.
View attachment 775627 1937 advertisment ^
View attachment 775628 1938 advertisment ^
View attachment 775626
Is the bike in this period photograph a 37 or a 38?
The rack would suggest 38.
My personal opinion, for what it's worth, is that the rack with the reflector looks better and is a nice safety feature to have, so it makes more sense to have it than not.
Unfortunately, there isn't a lot of hard proof to prove otherwise, so for now, it's, 37 with the reflector, and 38 without.