Thanks so much for this info. I have one more somewhat naive question.

If you arrive and depart on non-Schengen flights, but your arrival concourse and departure concourse are the same, then is there any need to clear security? I'm asking this particularly for my mom's return (MAA-FRA-YYZ). While the MAA flight usually arrives at C and the YYZ flight usually arrives at B, in looking at the flight histories, for example, on July 6, the MAA flight arrived at B48A and the YYZ flight departed from B25. In such a case, would one need to clear security?