The coin from Valens has an obverse legend that is only attested for gold and silver issues in RIC. The obverse reads D N VALENS PER F AVG, so instead of the normal P F, which is translated as PIVS FELIX, this coin has a legend that seems to be PERPETVVS FELIX.
The field marks Θ, Φ, Κ are not even recorded for Valens, only later when Gratian was a ruler. See RIC 49 for an example from workshop B with the same field markings for Gratian. The Gratian example is also very rare (r5).
I was hoping this was the first example discovered, but with minimal effort, I found this page with another example. It is the same workshop, but a different die.
https://www.cen-numismatique.com/a-new-bronze-of-valens-for-antioch-to-378-apr-j-c-by-renato-campo/
