Mark/Duncan
For most of the first century of its existence the Royal St David's Golf Club was referred to, not least by it own members, as 'Harlech' far more than by its extended and dignified moniker: my father and uncle, who numbered about 140 years of membership between them, always referred to 'Harlech', as did e.g. Bernard Darwin and Henry Longhurst when reporting on activities there. In my capacity as the club's historian I have always thought that greater use of the RStD label came with the increased emphasis on national and international marketing amongst golf clubs everywhere, and a sense that the 'royal' brand was especially helpful in this context. The artisan section, which finally expired in the early 1970s, was officially the 'Harlech Town Golf Club'.
There certainly has been confusion in the past: sadly two competitors for the 2009 Ladies Championship failed to register in time and were disqualified, having gone first to the historic city of St David's in Pembrokeshire and reported to the St David's City Golf Club (several times mentioned on this site). Likewise, an official R&A publication of the early 1990s promoting various championships to come put the RStD flag on the Pembrokeshire coast.
But as with Deal, I honestly don't think that any confusion is a big deal, and certainly a less big deal than the absence of the full historic titles of either - both of which are truly fab places for a game of golf.