Interesting, but objections might arise.
I'd say
Indulgentia is not specifically a tax reduction, but a favor of any sort.
Melville-Jones cites the coin of Patras recording the granting of permission to issue coins as an imperial favor,
INDVLGENTIAE AVG MONETA IMPETRATA.
The goddess on the
lion is not
Indulgentia herself, but Dea Caelestis, the chief goddess of
Carthage, representing the city, the recipient of the emperors'
generosity. In the same way I think the INDVLG FECVNDAE
type depicts the recipient of the
generosity, in this case the whole
Roman world, not
Indulgentia herself.
The curule chair is explained by my suggestion, since only
Roman citizens could obtain curule offices, but remains mysterious if the reference is to tax remissions. Plus, we know that
Caracalla granted universal citizenship at around the time that the INDVLG FECVNDAE
type appeared, but we hear nothing about a lowering of taxes important enough to be commemorated on imperial
denarii, at this time or any time during Caracalla's reign!