I think I see where you're going, and an upgraded rare can still end up ancient.
Only the Convert Set Item recipe will never roll or allow an ancient. And that recipe doesn't work on two-item sets.
Actually, I was just wondering if he threw more materials at the problem or more time? I am missing an ancient belt for my current build and an ancient Compass rose/TP for the Firebird push build. I need to level a bunch of gems too. I dunno, after I got the stash tab this season has lost a lot of luster. I did get to learn to play with a class that I don't normally use and that was fun. I do now have a bunch of inventory to manage again once the season ends.