Your conclusions about what I have said and what you have seen are on the right lines but not quite accurate.
Yes, there were many better quality Strathearn canes as well as many not so good ones. A later weight might contain all not so good ones, or it could be full of only better ones, or a mixture, in varying degrees, of both.
And also, if known early Vasart canes are seen in a Strathearn weight, it might still be an older (mid 60s) or a later one (late 70s to 80). The early Vasart canes, from the 1940s (and, dare I say it, [well, I will say it at Perth!] perhaps even the 1930s?) are found in items throughout the whole period of Vasart / Strathearn and are also seen in what I believe to be other, and even later, studio work. Those canes travelled around a great deal!
However, I cannot say beyond doubt that canes which I, and other collectors, consider to be later Strathearn cane types, are always so. It's a bit like discussions, over the years, on "Vasart" versus "Paul Ysart" canes - we are now realising that there were lots of very good quality early "Vasart" ones.
Regarding your question about a book (to assist with dating of Strathearn weights?), even the excellent coverage given by John Simmonds in Paperweights from Great Britain, 1930-2000
(which includes a listing of most of the Strathearn design numbers) and by Bob Hall in Scottish Paperweights
do not cover details that offer much help with dating by visual means.
This is why I would really like for somebody, some day, to provide a whole range of dated Strathearns from which we could collate a sizeable table of the canes. That might help - or it might prove nothing. Whatever it might do, it will be a massive undertaking :!:
In the meantime, do make use of Richard's galleries. His ordering by dateable items is very useful and is the beginning of what I mentioned for tabulating the canes. But I will agree with anyone that it is not easy, even with dated categories, to discover whether a particular cane or cane type was, or was not, used in a particular period.
Oh, isn't it fun