The rifle looks damn nice for what it is, early Amberg's are not common and this one looks totally original (though depot re-numbered bolt, which is not a huge deal, - factory would probably double value, but they are so rarely seen that its rarely an issue). Of course it passed through a collection center/depot (Cologne, which seems to be one of the most active, or at least that examples have survived in larger numbers), the unit marking disk has the C/R which suggest this is not only original, but the side the unit marking would have been applied (meaning not likely flipped). Looks like there might just be grease and crud over the disk, perhaps with a close examination or gentle rubbing it might reveal a unit marking. This early it really should have one.
Looks like you did well on this one, at least the rifle is worth picking up if the price is reasonable...