A possible error?

I have an official 1978 Oktoberfest mug which I purchased directly from the Rastal company's showroom. The signature on the bottom does not match same mugs I see on eBay and other internet sites. I'm trying to determine if there was an error in printing, on the mug I have.

My mug has the following signature (picture 1) Entwurf von Rupert Stockl.

Mugs from internet site are signed by Cornelia von Seidlein (picture 4)

Any help would be appreciated.