Early-mid 90s Saracen MTB frame sizing

Hi all,
I've been offered a Saracen frame and forks dating I think to around 1994 (with the 's' at the end of the top tube) which is claimed to be to be 16.5 inches in size. A quick scan of the Saracen catalogues on this website suggests that Saracen may never have made a 16.5 ins bike for this design. The frame size for this bike was apparently measured from the bottom bracket to the top
Of the seat post. I suspect that Saracen bike sizes may have been measured from the bb to the centre of the top tube on the seat post and as such this bike may only be a 15.5 ins bike?
I'm trying to buy a Saracen of this era to rebuild for my wife to use who is 5'5 ins and am thinking this size bike may be too small, though is suspect a 17.5 may be too big. Seems a challenge to find one to try in our part of the country! Any help on this question would also be appreciated! Many thanks

Re:

I've got a 1994 Kili XTR that I know for absolute definite is a 19" as I've owned it from new and I also have a Ti Kili Ultra, also a 1994.

Just measured them both and they both measure their respective sizes from BB centre to top tube centre.

Hope that's useful.

Re:

Many thanks for that, very useful to know how they are measured. Just need to work out if it'll be too small! Thanks agian.