Ian's passport shows an alias of "Ian Montgomery" at 13:17. However, when Hank looks at the same passport at 15:24, he says, "Ian Harmon." There's no reference to "Ian Montgomery."
Ian Harmon is on the run, and his alias 'Lester Cullum' has been lost to both his assassins and the police. So he turns to his friends for another fake passport in order to make a new escape. Only that new fake passport clearly bears the name... Lester Cullum.