Yes, it is Fine Cut Rings Variant - and yes, there are two variations on that pattern. There is no information on my website about it - but there is a huge amount of original research on the pattern where it is illustrated / written about at length in our NetworK journals, number 4 and 5, and also on page 152 of my "Century of Carnival Glass".
The design number was registered by Guggenheim in London (a wholesaler / agent) in 1924 , but we have not found any records to trace it further back than that. Every piece I have seen has the RD number. The maker is not confirmed (despite the RD) but Leerdam of Holland is in the frame (but the style could be Rindskopf too). It is European for sure.
In "A Century of Carnival Glass" we show a 1928 ad from the Pottery Gazette which shows the exact celery you have, Sue (without the "fine cut" detail) - this is the Fine Cut Rings Variant. The RD is also shown on the ad. In our NetworK journals we show a 1925 ad which depicts an item with the "fine cut" detail. That one is Fine Cut Rings. And for the record, the "fine cut" effect is of course, simply the effect of the pressed pattern, as Christine suggested.
Glen