Usage examples of "Open Source" from 1993 and 1996:

https://groups.google.com/forum/#!msg/comp.os.ms-windows.pro...

http://www.xent.com/FoRK-archive/fall96/0269.html

Especially that Caldera announcement for OpenDOS seems fairly high-profile.

I'm not suggesting that Christine Peterson is lying when she claims to have coined "Open Source"; it could be coined independently on several occasions, or perhaps she had seen the term but merely forgot about it.

Even if OSI would have coined the term, that still wouldn't mean they should be in 100% control of all usage of it. That's not how language works.