There cannot be another Grandslam Winner because there is no Third Tier title to win ala Cruiserweight title and Euro title and Hardcore title etc.
You don't consider the ECW title a title?
CM Punk: ECW Championship, World Championship, Raw Tag Team Champion, Intercontinental Champion.
That's 4 Championships right there, I think all in a year's time. (?)
I don't think it matters either way. Wasn't "Grand Slam" a name used specifically for World, IC, Tag & Euro title holders?