An interesting error and a nice specimen!
RIC (
Mattingly 1938) and
BMC (
Carson 1962) should have known of this variant, however, because there were three such coins in the
Sofia portion of the
Reka Devnia hoard, published by
Mouchmov in 1934, p. 134, with one illustrated on pl. V, 71, from different dies than yours.
Mouchmov read the
rev. legend as LIBEPTAS
AVG, with the Greek P replacing the intended Latin R.
His photo seems to confirm that reading, but confirmation would be needed for the other two RD specimens, difficult to obtain since the
Sofia National Museum refuses to show its RD coins!
Another specimen is in the Dr. Erich Roth
Collection at Düsseldorf University, published by O. v. Vacano in 1990, no. 745, pl. 29. This example seems to share its
obv. die with the illustrated RD specimen, but its
rev. die is different and doesn't match that of your example either.
LIBERTAS is clearly spelled with the correct Latin R on the Roth coin. Yours also seems to show
LIBERTAS, though the crucial second
leg of the R is weakly struck.