That's the same loophole I found in the meantime. Locked threads remain in the thread creation history, so they can be found if you know who created the thread you are looking for.
The problem with wiping threads is that there are circumstances where even good threads with useful information can get locked, such as:
1. A group of people starting a fight and derailing a thread to the point where the mods shut it down.
You could ask the one moderated for the link in their moderation history
Edit i know that is hard work with the size of yours