The situation is more complicated than that though. The apparent vagueness is not a sign that there is wiggle room, but rather that there are existing contradictions the author didn’t manage to resolve. The reason the origins of the Orcs changed so often is because Tolkien laid down some pretty hard boundaries in his world as to what it meant to be an Elf/Man/Dwarf, what Melkor was able to do (not capable of independent creation), free will existing, Orcs always being evil, and his desire to maintain consistency with his Catholic faith regarding salvation.