My earliest memory of it was circa 1990 when we had problems getting source code out of escrow for a system, and we were advised to make sure the next system was open source.
Edit: Check this 1993 document by NASA: "National security and national competitiveness: Open source solutions; NASA requirements and capabilities"
OK, maybe, it was the first one I came across. Well, you can claim they invented the term in 1998 and I guess I can't convince you otherwise unless I dig up some old documents, which is unlikely.
Anyway, FWIW, we used the terms "open source" and "open source code" way before that and it was widely understood. I don't have any reason to make that up.
> Anyway, FWIW, we used the terms "open source" and "open source code" way before that and it was widely understood. I don't have any reason to make that up.
Perhaps it was your personal jargon. I don't see any evidence that it was widespread before 1998.
I think it's more likely that your memory is failing, and OSI's campaign was so successful that they really convinced you that you always called it "open source". It has been close to two decades, after all. We can forget.
Edit: Check this 1993 document by NASA: "National security and national competitiveness: Open source solutions; NASA requirements and capabilities"
https://books.google.fi/books?ei=8YMJVZ6-IIOhPaj8gMAO&id=zYQ...