I'm pretty sure he is referring to Sandy Koufax.
I don't see how that, if it were true, would add to the value of an autograph of the greatest lefty to ever pitch.
It's hard to choose between Koufax and Spahn. Koufax didn't play long enough and the first half of his career was not even close to what he was in his last six years or so. 1963
Spahn on the other hand probably stuck around two years too long.
A couple of the old timers can chime in on this but didn't Warren Spahn lose several years to WWII. If so, that probably robbed him of a couple of very good seasons.