Originally Posted by
SDQBound
EU Citizens usually go through the automated border control, so no stamp. Permanent residents normally go to an agent and depending on the agent's willingness, they will stamp it or not. I had to make a strong case at CDG once to get a stamp since the agent and his supervisor both concluded that I didn't need one.
Fair point, for some reason I had assumed OP to be non-Schengen resident (the Location: Belgium bit might have tipped me off
).
No idea if it's possible to get a Schengen exit stamp as Schengen resident/citizen (you don't have to use the automated gates, can always see an agent).
In any case I'm sure the issue is a Schengen exit stamp, not the Mexican one, as the Mexican one would presumably be on the same day (or the day before - are there overnight Mexico-US flights?) as entry to the US, therefore useless to prove 14 days since exit from Schengen.
(In fact, the *entry* stamp to Mexico would be more useful here.)