Thanks SO much for the convenience, Chek!
As for the the first one, I'm not sure. But, I believe the Rum confusion may be due to, as one user put it, the way different members of age see him. And have seen elements of his physical skill, body language, authority, etc.
The third seems to me as if Scotch and Rei had some sort of friendship or something in the SP, possibly, again, as a user suggested, he helped him or guided him after infiltrating the Org. where Rei apparently grew up in. Then, around the time of Shuichi's infiltration, Scotch's true affiliation was found out, and Shuichi was possibly forced to kill him while Rei watched, earning his Rye codename, but Rei swore that he would never forgive him.