To anyone who ever questioned this, I'm very convinced that you don't have to lay the final blow in order for TH to take into effect.
I was with my LS last night in Crawlers Nest hunting Exoray Mold for Renkei I. We weren't getting drops, so we decided to let our lvl 65+ Ninja solo the exorays and what do you know; he gets the drop... 20 min later, we tried it again, got the drop. It was very sketchy at this point, so we tried it a few more times, no dice though. Weird how it works like that.
2/4 solo on exorays and got an extremely rare drop.