I agree the tip should be as if everything was as it ended up, UNLESS the problem was not handled properly.

The comment about EC 2-4-1's is as the book suggests, HOWEVER some places run weekly 2-4-1 as they over price their food. At these places I modifly the tip to reflect a realistic comparable price. If you would not eat there unless the coupon existed, because of the absence of value, then I believe in moderation and equivalency in tipping.

THIS is NOT the case with all EC places, just some that also run regular newspaper specials. They continue to exist only because of the specials.