Just came across this thread
Interesting, I had the same experience with (don't mock) a schwagg plant I recently grew (see my sig below for the full grow report).
https://www.rollitup.org/grow-journals/584136-mexican-brick-bagseed-growing-out-2.html#post8269002
I don't really know the genetics of this plant for sure, but I think its a safe bet that its from commercially grown Mexican circa '99 or 2000. Buds were purchased as schwagg (not by me) in NY area around that time.
Trichomes never turned brown/amber. . ever. Eventually chopped it at about 12 weeks flower. By the time I did, it was foxtailing and still putting out new buds. I didn't mention in the thread, but by this point most of the fan-leaves had yellowed, and were removed.
My take on this is that after the calyxes swell, and the pistils mostly go brown, and the fan leaves are yellow, you're done, regardless of the trichrome color. Amber trichromes are just one sign of maturity, and not every strain shows it.