I think November 1963 is still the latest date stamp associated with a pre serial keystone badge. I've got a Jazz Festival date stamped [COLOR="Red"]Nov 18, 1963[/COLOR] with no serial number, red felt, and a baseball bat muffler (damper control).
As far as the changeover of alloy it isn't an exact date. It is a transition period of unknown length. A metal shelled drum (be it SS mechanism or P83) without a serial number has a higher probability of being a brass shell than one which has a serial. But we don't have accurate estimates of the probability. The same goes for baseball bat vs knob muffler, and the other hardware details people come up with. There are no absolutes, just probabilities, but we don't know what those are. And as we have learned repeatedly over the years, with Ludwig "never say never".