Hi Vfox and everyone. I've wondered this myself. The oldest coins that I have found with consecutive dates are ancient Judaean coins. The Roman Prefects Caponius (6-9 AD) and Ambibulus (9-12 AD) had dates on their coins.
For example:
LM-Theta= 9 AD
LM=10 AD
LMA= 11 AD
Unfortunately the only example I have of one of these is hardly worth showing because it was struck so off center and worn that the date isn't even on the coin.
James