Yes, I remembered the old archive. It was archived by threads. I remembered the announcement a few months ago.
In fact, both the old and the new archives were archived by threads!
The old archives were archived by message. I switched to threads mostly because my host imposed a limit of 60 seconds for a script to run, and the index script I had took about 3 minutes to index 25,000 messages. It took quite a bit of programming to get all the original content organized by threads. Once done, the index took less than a minute to index the same text. This is mostly because a lot of the extraneous HTML was omitted from the threads view.
At one point, I guess I copied the threads view to the standard archive. I didn't remember doing this. When I get time, I will clean it up.