Honestly, on the situations where I’ve gotten to see the pieces first hand, and/or after discussions with the owners......... I’d say most of the time I’ve narrowed it down to a problem with the cam, or break in, or oil.
I can only recall one instance where I was really confident the lifters themselves were the reason for the failure....... and in that particular instance....... it was pretty obvious.
That was right near the beginning of the whole lifter debacle in the early 2000’s.