Trier indeed made better specimens than Cologne. However, you put under the coin from Cologne that it was minted in 262. According to The Study that I read, this is not possible. Postumus would not have opened a mint in Cologne until 268. If you find it interesting then I refer you to Jerome Mairat "Coinage Of the Gallic Empire" (2014) This is available for free. He gives an extensive representation of the possible places where Postumus and the other Gallic emperors minted their coins.