"I've often wondered if any listers know of other bike frames that were made like the Professional Mk IV with the oversize oval plates that finish the top of the seat-stays? They seem so odd, almost as if the factory didn't want to take the time to grind the plates flush. Yet, I doubt this reason since this was close to, if not, their top model. "..... Jack Romans
I haven't seen one of these Raleigh Pro's in person (and always thought the fastback stays looked cooler...), but, Raleigh also used this unique method on the T.I.-Raleigh Team bike that I have.
My bike is a '81 or '82(estimated), built with 753 tubing. When I got it a couple of years ago, those seatstay caps got my attention too! Darned near got out a file to tidy it up myself. :-) Somewhere I read that this method was used on the 753 frames in order to reduce the amount of heat used during brazing. Might have seen this in "The Custom Bicycle". However, based on Curt Goodrich's article in the Riv Reader on seatstay treatments, this seems unlikely (if I'm remembering this wrong, please correct me).
So, the Pro wasn't the only bike with this odd characteristic, but I'd guess that only Raleigh was doing it. For production frames, there's little effort made to file and clean up, and I just assume that Raleigh was having these caps stamped out of sheet metal and quickly brazed on.