For those of you waiting to interview or about to have your interviews, I figured my experience may help.
I interviewed with an alum who graduated ~20 years ago. It was in his office and very conversational and laid back. He prefaced the entire discussion with "So Columbia makes me ask these really strange questions.. but I'm going to put them aside for now." That definitely set the tone for the rest of the interview!
He was extremely supportive and gave a lot of advice about his Columbia experience and what I shouldn't miss while there. The only standard questions he asked were the famous "ethical dilemma" question and "how do you work in a team?". No "Why Columbia?", "Why an MBA?" or anything like that. I threw in as much of those answers in our original discussion so he may not have needed to ask anything else. In fact, we spent the majority of the interview heading in tangents about my chosen industry and we debated back and forth on that topic (but it didn't feel like he was trying to probe my knowledge, just basic curiosity)
Anyway, for those of you interviewing with older alumni, just be aware that they may not directly ask you the key "admissions office set of questions" so find other ways of inserting in those answers. It certainly did throw me off in the beginning, but in the end, my interviewer told me that he'd write me up well. I know that this entire process is brutal and great applicants are getting dings, so I'll just keep my fingers crossed. Good luck to the rest of you out there!