Update: I've exhausted all possible avenues for any further BTC recovery, of that I'm certain

On LoyceV's advice, I did spend time in recent days claiming my various BTC forks, which means I now own ~0.5 in each of BCH, BSV, BTG and BCHA

For anyone who happens to discover this thread in future, please do follow Loyce's guide here - the original post is a little outdated in terms of which currencies are worth pursuing, but much of it still holds up. If you can tolerate a few hours of tinking with various wallets, it might be well worth your time: https://bitcointalk.org/index.php?topic=2836875.0