Hi,
RIC 4, is older, in many ways, than the 1949 publication date. In the preface it is noted that it was largely completed in the early 1940s but delayed by the war and the authors admit it was hard to update.
The question you ask of Milan/Rome is easily dealt with. The initial
attribution to a
mint other than
Rome was made because of the unusual
IMP C C
VIB...... for Trebonnianus Gallus etc but also included
Trajan Decius and family in the broader
attribution that did not fit the
Rome pattern of coins so
Milan was suggested as the centre of production. Subsequent
work has shown that there are known hybrids with confirmed
Rome mint types and the chances of a
cross mint hybrid occurring is much less likely than a single
mint of origin.
The original paper on this is K Elks, Reattribution of the
Milan Coins of
Trajan Decius to the
Rome Mint, in
Numismatic Chronicle 1972 pp 111-115. There is also
Robert Carson's paper, Mints in the Third Century, in the festschrift for Humphrey
Sutherland, Scripta Nummaria
Romania, 1978, pp 65-74.
Regards,
Mauseus