Valentinian III Debate

That is a poser. Do you know what the difference is supposed to be between the two?

Here's the problem. CNG lists this coin as a RIX 2010, however a very qualified authority, has said it is a RIC X 2018, due to the way the tail of the snake is coiled. However I don't have his paper yet to review. CNG stands by 2010.

Expert explanation:
What follows are the major regular issues. Normally the reverse breaks VICTORI - AAVGGG, but I know of a number of 2011 and 2018 specimens with VICTOR - IAAVGGG (there was one in the recent NAC auction). These were not known to Kent.

—2011/2006 - facing left foot (Val's left foot), tail loops across itself then contines behind leg in single piece, normal victory with blob behind for dress
—2010/2005- foot ditto, the tail opens up at the top creating a single length with a kink in it (the loop edges can be apart or touching), dress ditto
Note that Kent's numbers are in the wrong order.
—2018/ x - foot ditto, the tail has broken off the loop so there is a half coil under Val and a separate tail off to the right, the dress becomes less blob-like and more linear
This is the one you see everywhere. They were minted in huge numbers between the late 420s and the early 440s. There are no known examples from Rome. I haven't included a photo since you have two already!
—2019/2014 - the left foot is now seen more in profile, the snake is the same, Victory's dress is now just a left and right parenthesis
It is at this point that production begins to wind down. 2019, 2019.1-2, and 2024/2014, 2015 cover more than a decade, yet are very rare in comparison to 2018. The regular engravers of the past decades now disappear and a succession of inexperienced engravers try their hands at making dies. Coins are about even from Rome and Ravenna.
—2019.1/x - this is a small series with a very distinctive obverse and a terrible reverse; this is not in RIC
—2019.2/2015 - ditto for the foot and snake, Victory's parenthesis dress is now attached at the top and open at the bottom
Kent didn't know of 2019.2, but I know of seven specimens. The poor engraving continues (as you can see). Rome strikes no further regular issues after this.
—2024/x - everything changes as a new engraver is brought in. He remains until the reign of Anthemius. Flat striking is now a major problem with the mint and many of these and those of Pet. Max., Marcian, and Avitus are much more worn than those of the rest of the reign. This is the only regular solidus issue that I do not yet have a specimen of.