EDIT: Apologies, I've just realised that the reason why both tables change is that I am deleting rows in my code... I have no idea why it took me so long to realise it, must have had a complete brain melt over the weekend.
I have made the procedure slightly more complicated but separated the lists into two separate sheets so that no data is being lost.
Apologies for wasting everyone's time on such a simple answer! Thanks again