Minyan not e/o follows up on return cards also could be the office was invited to the chuppah or simchas choson v’kallah so no returns.
Goq, really really really really invitations do get lost in the mail. Lately it has gotten so bad many many people hand deliver those they can, not to save on postage but because then they know it got there. I can’t imagine a/o inviting e/o in an office and leaving one person out. even if you couldn’t stand the person you’d still invite them because you would look so awful.