here's the Pirkenhammer current site - it's not so user friendly but you can at least get their address or e-mail address. I think that should be your next step. You might ask them if the Papal Porcelain was widely available in the USA and where a person would have acquired it.
http://www.pirken-hammer.com/ads.htmlI'm still looking for an e-mail address for the Vatican. I did learn on the V.'s official web site that each pope is free to decorate his private apartments to his own taste.
Oh, and correction to my earlier post: Benedict XV wasn't German. He was Italian. B. XVI is German. Sorry. #6719 is a pattern number. Consistent with the e-bay plates, yours, and the pic on replacements.
KB