"Personally, I just call them all
antoniniani absent any evidence they were monetarily different at the time, and not knowing the ancient name used for these coins (a universal scholarly frustration)."
I think pre- and post-Aurelian's reform radiates were monetarily different in a significant way. That's why we recognize the coin reform of
Aurelian. That's why "
XXI" was added to the coins. I think the difference was
still relevant at the time of
Diocletian's reform and even later, at the time of
his Currency and
Maximum Prices Edicts of 301.
(I don't think anyone uses "aurelianus" for "XI" marked coins. They appeared under
Tacitus (after
Aurelian) and are very
rare and played virtually no role in the coinage system.)
We don't know the ancient names of the 3rd century
radiate so we have been using "
antoniniani" for coins of
Caracalla, coins of
Gallienus and
Claudius II, coins of
Aurelian pre- and post-reform, up to coins of the reform of
Diocletian. But, obviously, they
had different values at the time. As collectors, we don't need to care about their ancient values--one word fits all. As scholars, we do care about the difference. By parallel with "
antoninianus" perhaps "aureliani" should be "
aurelianianus," but it a made-up word either way and I prefer the shorter and simpler version which is clear enough.
Among collectors, it is accepted that the pre-reform radiates of
Diocletian can be called
antoniniani as they have been for many years. But, if you want to understand the coinage of
the tetrarchy it helps to distinguish coins with low, but significant, silver from those with very little or no silver. Post-reform radiates (a.k.a.
radiate fractions) have no added silver and are, intrinsically, worth their copper, whereas the 3-4% silver of the "aureliani" makes their intrinsic worth maybe 4 times as much. I believe the older "
antoniniani" of
Claudius II were regarded as different from aureliani and of lesser value.
Scholars don't know for sure the nominal values of the post-reform
denominations of
Diocletian, but it is thought that the Edicts changed the relative values of some of them. I, personally, think that the
post-reform radiate started out as nominally equal to the aurelianus (both 2 d.c.) but was later adjusted to half by doubling the nominal values of the other
denominations (the aurelianus became 4 d.c. while the
post-reform radiate remained 2 d.c.). Some think that coins of
Claudius II might have then been 1 d.c. I do not know if they were circulating in 301.
So, in summary, I think it is
fine for collectors to use the term "
antoniniani" for "
XXI" coins of
Diocletian, as they have for many years. However, if we want to distinguish pre- and post-reform coins of
Aurelian, as the ancients did, then we should use different terms for them.