Oops! Right you are. Silly me, my computer-addled brain starts counting from 0 instead of 1, so I turned on airports 0-24 and then midoriw (who writes entries for the MileageBrain blog among other things, and is decidedly less computer-addled) posted a list of airports 1-25. YUL was #25 (so technically the 26th airport).

Anyway, long story short I done goofed. I've re-enabeld YUL but it will take about 24 hours for fresh information from YUL to trickle back into the system. Good catch!