In case you are not already doing this, use a ball of the removed gum tape like an eraser to pick up gum tape residue. I’ve never struggled doing this on a well polished surface. Flash tape as soja suggests is a good alternative to re-polishing the mould.
Thanks for the endorsement Jonty in most cases when we design the mold edge the last few inches are not really used, once you pull it lay new tape down for your next part run