If the right wheel came on your Mar 55 car, VW didn't put it there. The spline change to fine happened late in 57 model year for the std wheel.
Afaik, semaphore cars did not get the canceling feature after a turn. So that would again mean it's a later wheel.
As for the offset of the outer rim to the center hub, your measurement is slight. It could have been bent that way after it was delivered. Or maybe VW changed the design a bit. I measured my 3 spoke wheel like you did and it's 20mm.
My wheel is a coarse spline, with the signal canceler, round rim profile. The guy I got it from said it was from a 56 CDN std.