"Local" catalogues, meaning those issued locally to the stamps issued are far more worthy of consideration when determining values.
For example, I recently bought this motor exhibition cover for a song. I collect neither post-war Germany or motor covers, but this was a true bargain.

The stamps are Scott German Occupation Stamps, 9N70-9N74, catalogued at $146.25 the set in 2008, no price on cover. However, the Michel 2004/05 Germany Specialised, Berlin (West) 75-79 catalogues the set at €200, or roughly $280. That's almost 100% premium.
I would imagine that Michel would understand German values better than Scott, or SG for that matter.
When in Rome and all that!