Graeme,
The March 1927 Spares List for the TS/CW models (non-illustrated) lists part number 1385D "Hub complete, back or front". Unfortunately further along it again lists 1411D as "Hub complete (Front or Rear)"! Just a few part numbers away at 1407D it lists "Hub shell only, T.S." Further along it again gives another hub shell as 1412D. There are no hub shells listed explicitly for the front and likewise explicitly for the rear.
While not being clear which is which model, other than the one hub shell mentioned, it is clear they intended the same hub to be used front and rear. Further it seems that hub was not the shared between the TS and the CW.
The 350EW should have the all pressed steel hub, no splines; one of C. Pullin's design contributions. The 600EW had the tapered spline from the beginning, and then a few years later certain 350cc models (I think the B29 was first) got the detachable brake drums with the tapered splines.
There are 100 splines or serrations.
-Doug