I found a nice article here on a web log:
http://tw.myblog.yahoo.com/kunson-home/ … amp;fid=32
The 金鼎商标 belonged to a man named 吴汉文 who sold ceramics. His pots, like many at the time which were custom made, had a company trademark seal on the bottom. The artist's name was also often included. His company, 吴德盛紫砂陶器行 was started in 1916. Until the late 20's his seal involved the three characters Wu De Sheng. He made the Jinding Shangbiao in the late 20's. His company went out of business in 1939.
I don't think there were any companies in the 1970's besides the number one and number two factories, however, they did make custom pots and copies of old ones (孟臣 for example)
Maybe someone has resurrected this brand, this sometimes happens. I guess they must all be copies if they are not from 1920s-30s, but I can't vouch for this article. I didn't do any other research. Let me know if you find anything else out. I had never heard of this seal before reading your post.