There actually was such a disclaimer on the Sam & Max Season 3 preorder page and the list of games that you could use the coupon on did not even include TOMI (even though the coupon actually works on TOMI, which led me to give a wrong reply in
this thread).
As far as I know, most if not all Telltale coupons only work on games released prior to the coupon being issued.
I've always bought every Telltale game (except for CSI and Telltale Texas Hold'Em) as soon as they're "pre-orderable", so I've only ever been able to redeem one coupon for myself (bought Telltale Texas Hold'Em with the Talk like a Pirate Day coupon) and I've used all the others to buy my brother (almost) every Telltale game imaginable.