I only did one Adventurer's league years ago (maybe pre-2018) and didn't know that. Do you have a favorite reference as to needing the 2018 or newer one? Or do the errata not go back all the way to the 2014 one?
What happens now if a player shows up with a 2014 PHB?
I don't think it's necessarily a standard, but it feels like it could be insightful as to how they're viewing the new version/printing/reorganization/whatnot.
It was posted earlier in this thread that if newer material contradicts older material, the newer material takes precedence. So, if you showed up with a 2014 PHB and tried to use something that had been errata'd, the newer printed PHB would take precedence.
Granted, it's not like the game has changed so incredibly radically that having a 2014 PHB would cause problems in most cases. I don't really track errata that closely, so, I'm the wrong person to ask.
My point though is that if we're insisting that the definition of "backwards compatible" is that I can use a 2014 PHB as is, in orgnanized play, then, well, that's already out the window and has been for years. The thing is, now they are flat out telling you what the changes are and that from 2024 forward, you can expect the OneD&D version to be the assumed PHB on the table.
It's not really all that unreasonable of an assumption, is it? This is not looking like a terribly enormous change. Mostly cleaning up verbiage and another kick at the cat to fix some stuff that's been considered not terribly well done for a long time. Plus, apparently, our 2024 PHB is going to have some new stuff in it too - new races at the very least. So, it's not like we're not getting some value out of new books.