For the query about further reading on Caithness weights, I'm afraid there is little to offer. The main reference is A Charlton Standard Catalogue, Caithness Paperweights 2nd edition
which was published in 2004. Although it covers all (?) the Caithness weights from 1969 to the time of publication, it sadly has mostly black and white images and only one image per weight. In many instances, the photo of a given weight leaves a lot to be desired and it can be hard to see the detail!
However, Frank's "Scotland's Glass" website does have a good range of colour photos and info on Caithness weights, but as far as I can tell, does not include the 1969 version of the Mars weight.
Allan's comments promted me to check the book and sure enough it's quite obvious that the original design for Mars (which was issued as part of the original 4-weight Planets set - and which were the first official abstract weights issued by Caithness) did not have a facet. So this faceted example even though it was presumably not part of an original set, is presumably much rarer than the ones that formed the limted edition of 500.