They don't always need a ramp/shim, particularly if they've been reset because the factory joint came loose.
You're right that there are other reasons why a neck might need to be removed, but we're talking about resets, right?
Guitars that need their necks reset generally need them due to the neck pulling forward.
The question asked was, "Whats the tell?," ie, "How can one tell if a guitar has had a neck reset?" My point was simply that if a guitar has had a neck reset done properly, there will be a ramp or shim or wedge under the fretboard extension to maintain proper geometry, and that's one way to tell.
It's true that not every luthier adds the shim, but uness they've compensated for the geometery being off (you can pull the frets, level the neck and refret, for instance) you're going to have buzzing or noting out around the 14th fret.
Re; other reasons to remove a neck: My D50 needed to have the neck block reglued as it had shifted due to decades of improper maintenance in a hot climate. That repair involved removing the neck.
I had Guild in New Hartford do the job, and though I didn't ask for the neck to be reset, they did it at the same time as they felt the the guitar needed it, and since the neck was off anyway. . . .