Burnett, A. & P. Craddock. "Rome and Alexandria: the minting of Egyptian tetradrachms under Severus Alexander" in ANSMN 28 (1983), pp. 109 -118 and pl. 20.
Burnett and Craddock convincingly prove that some Severus Alexander tetradrachms bearing regnal years 4, 5 and 7 were minted in Rome for use in Alexandria.