As I remarked, many (perhaps most) SPQ necklaces have been restrung and changed. Without knowing a specific history, I would have to date a necklace as "recent" based on the lines used. Any construction, as likely as not, is going to include a hogepoge of beads from different times. It would be abundantly easier to give the beads, group by group, a time range.

But trying to date such a necklace is practically pointless.

I, myself, have restrung a number of SPQ necklaces—and I have altered them to the specifications of the client.

JDA.