When I entered the code, it only mentioned that I'd get 50 bonus pts with my next title (I didn't check the counter to see if it instantly jumped 50 pts).
Last night, I entered the Bridge to Terabithia copy I got with that promotion a few months back, and it looks like it actually gave me the full 100 bonus pts.
TL;DR: Don't trust the message on screen. Look at your points history.