Compatibility with PUC Lua versions after 5.1 is especially hard, given that more or less arbitrary syntactic and semantic but also C API changes have been introduced in every version since then.
That is mostly the reason why LuaJIT is stuck with a mix of 5.1 and toggled 5.2 features.
That is mostly the reason why LuaJIT is stuck with a mix of 5.1 and toggled 5.2 features.