I myself have never owned a genuine Waterman lever-filler overlay over RHR, and in over 20 years I've probably seen no more than three or four examples (including sets). And let me clarify: though assembly of fakes was definitely under way by the end of the 1980s, many more were made in the 1990s -- though I think things slowed down mid-decade as collectors got wise. In fact, resale prices on these pens dropped so far that many collectors picked them up as fantasy pieces, simply because they were so cheap -- in many cases with hardly any premium over a regular BHR example.
As for authentication, there are a number of telltale signs found on the assembled pens, but it should be noted that a really good faker could assemble a pen that would pass. So provenance definitely counts here. Virtually all the fakes I've seen have the overlay slightly loose on both cap and barrel, with the number at the end of the barrel incorrect in one respect or another.
Thank you very much for your reply. I've looked at this set several times since your first reply trying to find something amiss and I don't see anything wrong. I looked again paying close attention to the fit of the overlay and it seems right. Since my first RHR overlay was a fantasy piece that the seller had made, I did know to look at the number and, of course 52 would have been a red flag. The 452 stamp this pen has looks very good and is properly centered. It's positively not a mark that the 4 was added to as that would be way off center.
I'm new to the FPB, but I've been collecting for about fifteen years and my collection is mostly Waterman including several overlays, nevertheless, I still don't consider myself a professional. I had read these pens were rare, but when you called them "extremely rare" it surprised me. I value your professional opinion. This set looks correct to me and your comment about it being a set made me feel better about this purchase, but I still can't help but question its authenticity. Somebody did a very good job if it's not authentic.