Are leads quest specific?

By Acolyte Rivan, in The Witcher Adventure Game

I don't know if I am missing something from the rules, but what happens to "leftover" leads after being turned in for proofs and the completion of quests? When you draw a new quest, are the leads you researched for your last quest equally relevant for the new quest? Have thought about having players either discard all leads when drawing a new quest or allowing one lead per proof to be kept if it corresponds to the same proof on the subsequent quest. Any thoughts?

What remains, remains. Unused leads and unused proofs are kept and carried over to the next quest