Getting back to nonetheless I have begun to wonder if it's an eggcorn. The OE was naŽylęs. While na meant 'no' or 'not' and lęs meant 'less', Žy only meant 'the' in the masculine and neuter singular instrumental. I'm thinking it might well have been some sort of word in its own right and only became analyzed as 'none the less' at a later date. Someone who knows more about the history of English would have to take it from here.