14/31 probably means #14 of the 31st. transitdocs shows them as, for instance, 14(31).

It's confusing, because if there are run-through cars (as with the Sunset and the Texas Eagle, though I think I saw somewhere they're not doing it any more), the Sunset west of San Antonio would be carded as, for instance, #1/21 (or was it 1/421) westbound. That's how timetable junkies in England could think that, for instance, Sanderson TX gets 2 trains each way, 3 days a week; the Eagle cars and the Sunset were combined in San Antonio and operated as a single train. I think I've seen the Builder listed that way, sometimes (8/28).