personally, i'd put down the old contact info and claim ignorance, haha. I don't think it's super crucial to be able to contact them, especially if it's an old experience or whatever, but if it's a letter writer, I'd say you really should have up to date info. I just covered my butt, by sending an email to the contact info I had on the experience and said I was applying to medical school, and it usually didn't lead to a reply back. I remember sending an email to the premed honor society i was in, in 2009, when I was applying in 2013, and some student just said "ok". If it's more recent, and something you talk about more, it might be more important to get someone who can talk about what you did, but it's part of a small part of your app in general. If you have the grades and the scores, they'll work with you to clear your name probably, like ask you about the experience in the interview or email you about it.