@Sig That particular model has been in production since at least the mid 90s, though I don’t believe it was made for very long. I’ve actually handled about 4-5 of them from various stages and of various ages but all had acrylic stems.
Sadly I don’t have decent pictures at the moment. This one is from the mid nineties early in the acrylic stem transition as denoted from the dot next to the S. It has a "softer" brown-tinted vario contrast, which is why I liked it (not that you can see from the dreadful picture) but I gave one that looks exactly like yours but with the same dot to a friend.
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The next image is, I believe, a close cousin of this shape, once removed. The main distinction being that the side facets are left smooth, not the front facing ones, and it also seems to me the cousin has a more convex bowl rim profile. The pipe above has a gentle curve to the rim, while the one below has a much more aggressive one. I don’t have them on hand to compare, but I also believe one of these two has a flatter shank profile along the bottom, while the other has a round one.
I don’t know if this qualifies it for designation as a separate shape? Regardless, I have seen this second variant smooth and stamped RO 25 - making it part and parcel of the other Facets like the hexagonal 163. If these are two different shapes, then the second one is, in my opinion, probably the candidate for shape No. 194. and most likely by Tom Eltang.
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I have seen them both in smooth and vario finishes. I have seen them mostly without shape numbers. I believe this has to do with when they were made, i.e. whether they were part of some re-issue, special line, or what have you.
To make things even muddier, there is also a very similar shape that is not faceted but round and has the same curved bowl rim and thick walls. This one had some cross-pollination with the Danske Klub line (can’t dig up the pictures for this one sadly) so I wouldn’t be surprised to see some of the hexagonal ones there as well.
I love Stanwell, but the (over)production in their heyday truly has made a mess of trying to figure out anything firm about the pipes.