If you're playing B/X, you are playing the version of Basic that went with BECMI, since it's the only one that got an Expert Set... And therefore, it's exactly the one in BECMI...
Sure. But there were tweaks with each republishing of Basic, to the point that RC looks quite different from the form of Basic we met in Isle of Dread.
My point was that these are all similar - iterative, compatible designs. Neither 1e nor Basic were compatible with OD&D, but 2e was iterative on 1e, and Basic’s variations were all iterative on what came before.
Player’s Option was iterative on 2e, but 3e was a hard break, using an entirely new core mechanic. 3.5e was iterative on 3e, and even Bo9S with its pocket ruleset that works more like 4e was iterative and built to be compatible with 3e d20 products. Pathfinder 1e too was iterative on 3e d20.
4e used the d20 system, but was a hard break from the 3e game mechanics in most ways. But each year of 4e showed how the system could accommodate subsystems that weren’t necessarily the standardised AEDU progressions from PH1.
5e was a hard break again, working to try to unify the player base (it mostly succeeded). And over at Paizo, Pathfinder 2e was a hard break from Pathfinder 1e as it used a system more akin to 4e than 3e.
They’ve already said this is not a hard break from 5e. It doesn’t matter what they call it - it’s going to be iterative upon 5e books. HOW iterative is an argument we really can’t come to a conclusion on because we can’t agree on how iterative the previous edition revisions were from their baseline editions.
So feel free to keep arguing that BECMI isn’t iterative on Basic but just the same thing. That’s literally proving my point. We can’t measure the iterativeness. So using terms like 5.25e based on a goalpost of Pathfinder = 3.75e is not really useful or provable, since Pathfinder’s differences from 3.5e aren’t “smaller” than 3.5e from 3e nor a halfway step between 3.5e and 4e. It was literally a fanon term created because they wanted to make the connection back to 3.5e and that was the only “decimal” edition.