The claim that folks inside the Empire lost track of what year it was because Denys got the date of the Incarnation off by 4 or 6 years simply isn't credible: the dating system in the Empire based on the 15 year cycle of 'indictions' on 1 September each year, dating to Diocletians reforms, continued uninterrupted (Anna Comnena uses it in her Alexiad)--the tax system depended on it, and one thing Romans, whether pagan or Christian did well was tax--indeed it's still used in the Orthodox Church for some purposes. Our Anno Domini dates for events in the Empire are based on a retrospective matching of the indictions with events dates on the A.D. system, so the 4 to 6 year discrepency is built into them, including the dates for the supposed cataclysm in 538 and the completion dates for all the edifices and iconography I've refereed to and would have been unknown in the Empire.
By every account I can find on the net, including those that report on the efforts to correlate the tax cycles with Dennis' system, the error is there.
I know you want to believe that the city of Byzantium was not subject to the cateclysm that destroyed most of civilization in 538 AD, but I'll tell you they sure must have missed out on the taxes they used to collect from the hinterlands.
Just saw a piece on the Colosus of Rhodes, and it was noted that the Arabs stopped and collected up the leftover bronze to make coins during their conquest.
Hmmmm. Such a thriving economy, eh?