I would contest this, based on the many discussions there have been on HN about this, as well as many people (including many "normal" software developers who are not deeply invested in open source) I've met and talked to over the years having only a vague notion of what "open source" is exactly (often being something along the lines of "you have access to the source code").

I'd be willing to bet a substantial amount of money that if you were to ask 1,000 random software developers about Open Source, the OSI, and the OSD over half of them won't be able to give you a coherent answer on what these things are exactly.

This is the crux of the issue, really. Who did or did not invent the term isn't necessarily all that important: the thing is that in common understanding it doesn't really have the clear specific meaning in the minds of most, whereas for others – I would argue a minority – it has a very clear and very specific meaning, which inevitably leads to friction.

I guess the point of "Open Source was used before the OSI came along" is to demonstrate that it's a term that has a kind-of "obvious" meaning, and has been coined independently of the OSI's coining more than once. People don't hear "Open Source" and then consult a precise definition, they hear "Open Source" and assume it means what it says on the tin. The same applies to "Free Software", a term with 15 years more effort to explain what it means exactly, with even more limited success.

It seems to me that attempting to educate a landmass about a term with an "obvious meaning" is a futile effort; there have been many language pedantics over the years, and I don't know of a single attempt that has worked out. You're welcome to try as far as I'm concerned, but it seems to me that there are many more fruitful ways to spend time and effort.