At the risk of bumping a necro thread to the annoyance of all (sorry) - Adding my recently acquired RIC 267a septimius severus dea caelestis with drum and facing head example for those that happen upon this thread.
Hi-res in the link:
https://www.forumancientcoins.com/gallery/displayimage.php?pid=187101As opposed to the more common thunderbolt version:
What I had noticed discussed above - the lion can also be either head facing or head right, and it appears to not correlate to whether dea caelestis' head is facing or right. The first coin I posted above has a facing lion head, the second has a lion head to the right - both are clear examples of this difference.
So in theory there are almost double the number of possible mix/match variations of the denarii reverses:
-drum, scepter, goddess facing, lion head facing, no exergue
-drum, scepter, goddess facing, lion head right, no exergue
-drum, scepter, goddess right, lion head facing, no exergue
-drum, scepter, goddess facing, lion head right, no exergue
-drum, scepter, goddess facing, lion head facing
-drum, scepter, goddess facing, lion head right
-drum, scepter, goddess right, lion head facing
-drum, scepter, goddess facing, lion head right
-drum, no scepter, goddess facing, lion head facing
-drum, no scepter, goddess facing, lion head right
-drum, no scepter, goddess right, lion head facing
-drum, no scepter, goddess facing, lion head right
-thunderbolt, no scepter, goddess facing, lion head facing
-thunderbolt, no scepter, goddess facing, lion head right
-thunderbolt, no scepter, goddess right, lion head facing
-thunderbolt, no scepter, goddess facing, lion head right
-thunderbolt, scepter, goddess facing, lion head facing
-thunderbolt, scepter, goddess facing, lion head right
-thunderbolt, scepter, goddess right, lion head facing
-thunderbolt, scepter, goddess facing, lion head right
And all of these are potentially available with the following reverses (all observed n this thread):
-Septimius bust
-Septimius draped
-Septimius draped and cuirassed
-Caracalla draped
-Geta Draped
-Geta draped and cuirassed
So in other words, there are potentially 120 variants of this coin in existence - though realistically not all of the rare reverses will be paired with the rarest obverses - in particular it is very unlikely that the draped or cuirassed Septimius obverses will be paired with every reverse variant on denarii.