ok I see. I put them together for a photo but not as if I were smoking them. They go down a little more.
BUT
The pipes work best with the stem they came with. And some sit much higher than others.
They all (including the Deluxe System) fit into what could be best described as a 1 Morse taper. If the end of the tenon was cut back a little farther, or the cutter was run into the mortise a little farther, then there will be a difference in the gap.
I doubt whether the person who is performing the operation is gauging the gap. Probably done manually and just to the point where the stem doesn't wobble back and forth and is secure in the stummel.
The whole idea behind the concept was that as the fitting wore (opened up), it would still seal and hold the stem in place, as the well had to be drained often, and that would necessitate removing the stem often.
I don't smoke 20 bowls a day in my a particular one of my Deluxe System, Pub or House pipes; It would probably take 4 lifetimes in order to wear the junction to the degree where the collar of the stem and end of the shank would eventually meet up.
So I guess if they do stick a bit farther, then they'd probably last for 5 or 6 lifetimes... I doubt whether somebody is going to single you out at say a pipe show and call attention how large of a gap is on your Pub pipe. But then there are some who often just have to pipe up and make some barely relevant, often BS comment...
And now you know the rest of the story.