Comp Cams/Delphi HFT lifters and the 'hardening line'.

I've seen lifters with the harder base material....some of my Opel (GM) engine lifters back-in-the-day were made like that. But IMHO that is just a design of construction, not one that is especially superior to other methods of construction; it just may be a hard base attached to a non-hardened body. So I think this is getting enamored of something that is not particularly special in the world of lifters.

Now the one lifter that is harder than the others may be an issue. But it also may be that it somehow has some oil in it and will not compress simply due to that. It is a simple matter to disassemble and examine the innerds.