This example on Wildwinds shows a RIC 120 denarius struck in 197-198 AD. Knowing that Caracalla was made augustus in 198, it may be one of the first issue with AVGG. VICT AVGG COS II PP
Here's the question... how about terminal Roman / Early Byzantine coins? Justinian I AV Solidus VICTORIA AVGGG Delta / CONOB Even though there were times that there was a "third" Augustus (Constantius III), I believe the last time that the East ever recognized three emperors was until the death of Arcadius. So why were three G's used on so many gold coins of the East? Did it evolve to have a different meaning, or were Byzantine celatores starting to forget Latin in favor of Greek, and more than a little rusty in their grammar? Another odd one are the late coins of Tetricus I: HILARITAS AVGG would suggest two emperors, but the evidence that Tetricus II was ever promoted beyond Caesar is dubious at best - a scarce set of barbarous coins, and one or two that *might* have been official. Perhaps he was trying to recognize Aurelian as a last ditch attempt to spare his life?
I couldn’t find that tremessis of Libius Severus III anywhere, but it supposed to have the legend : VICTORI AVGGGG !