The OSI are the people who made it up, and the only reason why anybody cares about it. If you call yourself Open Source and you don't comply with the OSI definition, you're a parasite trying to commit fraud with the good will generated by other people.

I also don't care if somebody in 1975 said "I like to be open, and I'll let anyone look at the source." Old McDonald had a farm before McDonald's was a restaurant, but that doesn't mean that if you open a restaurant called McDonald's that is decorated like a McDonald's, you're not a scammer. I know your plastic fruit is carbon-based, but if you label it as "organic" you're a thief.

If you're not trying to scam people, be creative and make up your own catchphrase for letting people look at your source code - or don't even, because the whole idea of having a branding for allowing people access (and rights to) the source is imitation of the FSF and OSI.