The link provided above drills down to the following, from 2019:
https://www.thatt206life.com/2019/03...th-rare-backs/
“There are 31 Portraits in the T206 set that feature a Hall of Famer. 23 of them were printed in the 150-350 Series. The rarest backs that were printed in the 150-350 Series are Old Mill and Brown Hindu.”
Most if not all of the cards listed above are portraits. I’ve never seen a Lajoie in that combo. The Mathewson combo has sold for a big premium in past auctions as well - very few of them.