What about coins? Nobody stopped making coins. What about the tree rings? Isn’t there a comprehensive pattern of tree rings that can provide a date for preserved wood for at least the last 2000 years, calibrated for volcanic events, etc.?
Tree rings tell ya nothin’, unless they correspond to, for example, a core taken from an old rafter in some structure that happens to have survived at least that long. There aren’t that many, as one would expect. Also, dendrochronology as used with RC dating (it was in use before RC dating was discovered) has taken a long time to get data for each given region, and this research takes time each place its done.
When there’s no wiggle-match with the existing data set (which is built on old living trees and older dead trees which overlap the living ones in age, and even older, deader ones which overlap those), my view is, there’s a bias at work, because the item being tested has already been dated based on a faulty chronology, so the dendrochronologists never bother to wiggle-match with (usually) younger data sets.
Coins:
https://www.pinterest.com/clchristinelee/dark-age-coins-300-1100/
tidbit from the Centuries of Darkness website:
https://www.centuries.co.uk/faq.htm#q3