Fair point Bernard, by putting 1950's, I was indicating that there was a progression between pre and post-war production that would have included a short period within the late 1940's. The evidence for this continuation of "Rainbow" ware was found by Jeanette Hayhurst some years ago and was particularly relevant if exhibiting at the NEC when it had a 1940 dateline for glass (it's currently 1950).
As for the pontil finishing. Since you have described the pontil as re-shaped I am assuming that you are referring to a wide, well polished, concave pontil that covers virtually the whole of the base?
There seems to be some consistancy as to the type of pontil that is used for a given series of wares, however, just as with other manufacturers, there are idiosyncracies that have, to date, not been explained. Your hypothosis that there may have been a particular finish for the more pricey items may well be right, but, since there have not been enough items placed together to give this credance, it is difficult to make any positive conclusion.
For instance, I have just bought a Keith Murray designed decanter by Royal Brierley that has a flat base. It is likely that this would have been an expensive item, but it doesn't have the 'deluxe'/ re-shaped pontil that you refer to. Most likely this would be because the flat base was more apt for the item in question.
The same variations between standard pontil, wide pontil, concave pontil covering the base, and flat base, occur across cut glass by S&W/RB. Standard and wide pontils occur within the art glass ranges, with occasional use of the style I have assumed you are referring to, which cover most of the base. Perhaps, at this stage, it is unwise to make any hard and fast 'rule(s)-of-thumb' concerning the finishing of S&W/RB's work, rather take note that a number of finishes were employed - making it a joy (or a chore) to diagnose!!