I have been selling Sauers recently imported from Sweden. I've seen about every boxlock you can think of. Only one gun I saw was loose, and that was an early fifties boxlock with no crossbolt. The guns that I have seen marked Eckenforde were also clearly marked Made in Germany. The east german guns are marked GDR from the mid sixties on. I've given up trying to identify a model number. I just put the proof date on them unless they are from Eckenforde. Then I identify them as West German.
My preference in these guns is alway the guns made in the 1930s. Their balance is superior and the fit and finish is nicer, as well as their engraving. Early fifties guns are almost as nice, no matter which side of the fence they were made on. By the mid seventies, Merkels, Sauers and Simsons all look so much alike that the only way to tell them apart is to read the names on the barrels. They all look like Merkels.
