Many European libraries have digitized industrial archives.
If your piece is listed in the 1906 catalogue but not in the 1912 catalogue, it was a short-run item. Short run = higher value. Cross-reference the original price (adjusted for inflation, a 5 ℳ item is roughly $50 in 1906 money, but the antique value today could be $500+). wmf catalogue 1906 pdf exclusive
Because the demand for a is high among 1,000+ daily searches from collectors, scammers have taken notice. Be wary of: Many European libraries have digitized industrial archives