[JimStinson]

There are at least a dozen considered tough to impossible. About 2 dozen which only a few examples exist of , topping my list of perhaps impossible (at least at present) would be
1) Jose Mendez
2) Cristobal Torriente
3) Frank Grant

nearly impossible
4) King Kelly
5) Tim Keefe
6) Hoss Radbourne
7) Buck Ewing
8) Addie Joss
and probably a few others. But the top three "forget it"

I was researching #1 & #2 over 18 years before their induction into the hall, And was never able (even then) to produce a single lead. And that included knocking on doors and even making "cold calls" and being armed with information that even today I've kept secret