I'm a come-back player (played 40 years ago, picked it up again a month or so ago). I understand that high range is more the player than it is the equipment -- but that doesn't stop us shopping for equipment!
Anyway, way back when I used to play, I could pretty never much hit a consistent high-C above the staff without a lot of struggle (usually because my lip would be shot after the half-time show -- that's my story and I'm stickin' to it!). When I recently started up again, I could hit the C pretty consistently -- but still have to work for it.
Anyway, I recently picked up a couple of old "peashooter" horns (A Conn 94B and a Kingston stencil). I was surprised to find I could not only easily walk up to the high C with every little effort (even using the cruddy mouthpieces that came with the horns), but could even continuing playing an entire scale an octave higher to hit the double C (although had to work a little for it)!
I haven't seen any mention of this peashooter characteristic before -- anyone experience something similar?