Were 'Non-Local' Medallions of the Valerianic Dynasty struck at the Mint of Viminacium?

In the most recently published comprehensive survey of the coinage of the Valerianic dynasty (AD 253-368), the late Professor Robert Göbl attributed just two unique bronze medallions to the mint of Viminacium, on the river Danube in modern Serbia. Both bear on the obverse the bust of an unnamed young prince, who Göbl identified as Valerian II, elder son of Gallienus, who held the rank of Caesar from 256 until his death in 258.