Nice coin and nice set! Say, that Procopius looks familiar! 
Usurpers are a dangerous slippery slope - you're missing Clodius Albinus, Quietus and Macrianus, and then you're getting into some seriously expensive territory.
IIRC, only Magnus Maximus and Julian II issued coins first as usurpers, then as legitimate emperors. All the rest (Vitellius, Vespasian, Severus, Pupienus/Balbinus, Decius, Probus, Diocletian) were "usurper" only for a few weeks or months until the last guy was deposed. IIRC none of them have any coins certainly attributable to a period of usurpation.
Usurpers are a dangerous slippery slope - you're missing Clodius Albinus, Quietus and Macrianus, and then you're getting into some seriously expensive territory.
IIRC, only Magnus Maximus and Julian II issued coins first as usurpers, then as legitimate emperors. All the rest (Vitellius, Vespasian, Severus, Pupienus/Balbinus, Decius, Probus, Diocletian) were "usurper" only for a few weeks or months until the last guy was deposed. IIRC none of them have any coins certainly attributable to a period of usurpation.

























