Hello Matteo, Peter
M > In brief Corfù thinks that the Achaemenid coinage could not be an imperial/regal coinage because it didn't circulate in the whole empire.
From this – it looks to me like the guy is just playing with words. Its long established that the coins seem officially sanctioned but only circulated in the coin-using Western provinces.
Since the gold darics were much used for paying bribes to Greek political allies, and also, they were struck, not to local Lydian weight standards but to the Sumerian/Babylonian weight standards established before 2000 BC, I would call them imperial issues – but arguing about use of words seems rather a waste of time to me.
While we are on this topic, I will mention a very important connected matter brought up by Kurke. It is the fact that no written text ever even mentions coins for about the first 150 years of their existence.
A guess about this is to do with the scandalous sort of popularism coin use was associated with, by the lights of the elite scribal class. We have no clear histories of this matter, history starts only after coins have been invented. But there are hints that the social changes associated with first coin use make the French Revolution look like a picnic in the park.
Rob T