Interesting, because
legend errors are
rare on
Roman imperial coins, and generally only occur on one die of the
type.
Such errors are very easy to overlook. Maybe more like yours will turn up, now that you have pointed it out and specialist collectors who read this
thread will be on the lookout for other specimens!
I think the wear on the
reverse die doesn't tell us anything, since that die may well have been used with other, correct,
obv. dies too.