I think it's even worse than that, luau and luaJIT have evolved in different directions than the official lua project, such that they are now all sublty incompatible with each others. They all branch from lua 5.1 but it feels like there isn't an offical standard anymore.

At the very least, there's a common core of Lua 5.1 that works across Luau, LuaJIT, and PUC Lua, so it's not as if there's no standardization here. We definitely aspire to include _more_ than just Lua 5.1 in Luau though.