Federico has exaplined the Officina/Workshops perfectly. They are identified by the Greek letters in this acse.
RIC bundles all these coins into the same
RIC Id. In fact there were nine
officina working in
Antioch during this period using A, B,
,
,
,
, Z, H, and
. The
is used in place of Theta, being the initial letter of Thantos, god of Death, considered to be unlucky. I have included an example from this
officina but
RIC 925.
The
XXI here is considered to be the value mark being either 21 or 20:1 is unclear.
Antioch also used KA as the where K=20 as in the following example if
RIC 920.
In other words you can generally ignore the
officina and value mark in order to get the
RIC Id. for
Probus, which is generally based on the
Obverse Legend,
Reverse Legend and
Reverse Devices.
RIC then lists the known busts, emissions/issues and
officina.
RIC does a fairly
poor job of completeing the busts, issues and
officina and examples regularly turn up that are not covered
inr RIC. All of which adds to my fun in collecting
Probus!
Regards,
Martin