It’s unlikely you have official “membership” in your college ministry, which makes sense. While I can think of some advantages to having something official along those lines, there are disadvantages too.
But one disadvantage to not offering membership is that it’s easier for students to fall through the cracks. If an official list indicated which students, at some point in the past, had gone “all in” with your campus ministry, then you could occasionally identify if they’re still showing up for Large Group or participating in small groups.
But again, you probably don’t have an opt-in “membership” list. But what if you created that sort of list anyway? And what if you actually used it every few months to discover anyone that might have come up missing (or might be involved less than usual). Those students deserve a contact, don’t they? They’ve been all-in with your college ministry; now you can be all-in with them.
I realize there’s some trickiness attached to this (especially figuring out who’s missing if your ministry is sizeable). You may not arrive at a perfect solution. But something intentional will beat the “organic,” we’ll-probably-just-notice-who’s-missing approach nearly every time.