We need an RPGsite wiki, with boilerplate debates logged for posterity. This would be an ideal candidate. Call it "theRPGSite knowledge repository and philosophical library".
The Old School R... (revival, renaissance, resurgence, regurgitation, retribution...) is one of several things based on a) who you're talking to, b) how much skin they have in the definition and c) how self-important they deem their opinion. Trying to define what the OSR is by anything "scientific" is a fool's errand. It defies definition. Like trying to scientifically define "the best chocolate the world has to offer". After you sifted through the 9 opinions offered by the 6 people you asked - you will still be left without an actual... definition.
1 - Some hold the OSR in a near-religious reverence as being ONLY the purview of older versions of D&D. Mentioning even "clones" or derivative works will have you declared a heretic and a crusade will be called upon your house. You will be tracked down, beaten, skinned alive and hung from a lamp-post as an example for other would-be heretics to behoove.
2 - Some hold the OSR in a more "gentlemen's club" reverence, where members play the older D&D and enthusiastically make clones and derivative works. As long as you stay within club guidelines (hotly debated during meetings), and your works bear a strong resemblance to the originals, then you can remain in good standing. I use the term "gentlemen's club" not in the modern sense of strippers but more in the Commonwealth old school meaning. To stay on theme of course.
3 - Some hold the OSR as a "playstyle". These are the Buddhist sects of the OSR, where one should strive for game perfection by employing the approaches and sensibilities of the Old Ways(tm). GMs don't pull punches. Players use their own ingenuity to navigate tough situations. Social interactions are from the players skill not from numbers on a sheet. You play to see what happens and GMs are encouraged to let things unfold based on how the players discover things, not in some pre-arranged level-appropriate theme park ride where you see only what you can handle.
4 - Some hold the OSR to be a larger preference for older games. These are the agnostic empathic near-do-wells of the bunch. They are fine calling any older game made in the 80's or early 90's, or any clones or derivivative works of these games to be considered "old school".
Some people are a mixture of different passions from these broad groups.
They all like to argue about who's the most correct, most pure and most likely to have been derived from the holy energy of the original creators (Gygax and Arneson) of which there is debate about which one of these chaps ACTUALLY created the game in the first place. So you could be an Arnesonian Hardline D&D Adherent who abhors clones and thinks D&D 2nd Edition was made by communists who successfully ruined the entire hobby or a more relaxed Playstylist Clonist Enthusiast who is happy to share their creative energies with the other OSR-like people in the room and tolerate the same.
And everything in between, outside, adjacent and even unrelated to any of those definitions.
So, basically, "OSR" has become a term that has been so muddied by all the various "religions" worshipping it - it's really hard to tell what it means or why the fuck we even care anymore.
Honestly, we should all stop giving a shit and just play the fucking games we enjoy playing. The real world already has enough tribes and cantankerous old grognard is already one of them! We already have a tribe folks! We don't even have to make t-shirts!
Just my two cents...