The 20th century – mirroring time in ceramics

Oops! "Dorothea Roth, vase, 1970-1975 Roth Eberhahn West Germany"

1970-1975??? Do they know something more? And the design by "Dorothea Roth" isn't confirmed as well as far as I know.

All I could find out until now is that Mr. Roth told me in a SHORT phonecall in 2012 that the company was founded in November 1969 and later registred in 1970. This phonecall is the source of the information you find on some internet sites. The design of the guitar shaped vase is documented 1970, but may also be designed earlier.

So how do they know "1970-1975"?

i don't know Ralf. Why don't you write a short message to Petra Mesken (she had informed me with a newsletter e-mail) and ask?:
https://petraonpottery.wordpress.com/author/petraonpottery/