"John Harrison" is an incredibly generic Section 31 name, along with "Harris" and "Sloan" (wait... Harris...sloan? Harrisloan? Harrison??? http://www.dramabutton.com
) so I can imagine it being given to another agent in a universe where Khan wasn't found and thawed by a mad Admiral in 2259.
Oh god, someone put a gun to Pocket's head and make Myriad Universes: Khan
happen! It would be awesome. I'd love to see that "What if the Botany Bay were found by the Enterprise-D?" story mentioned in the very earliest of mentions of the Split Infinities