I've skimmed through thread, and now I need a drink... holy cow.
Okay, so I haven't worked for Schwalbe for a few years now but unless there has been profound changes at the company (not likely), Schwalbe internally relies solely on the ETRTO system of tire measurement. Any other measurement numbers published in the catalog or on the sides of the tires are secondary to the ETRTO #. So, a 37-622 would measure 37mm wide +/- the stated tolerance (I think 3 mm). Much of the +/- relates to the fact a given width of a tire can fit on a range of rim widths; a wider rim lets the tire sidewalls spread out a bit more producing a wider measurement when mounted.
Now, after writing this, it seems as though the need for an exact measurement has been mitigated (if the fenders have been ditched), but generally speaking if the width tolerance is 37mm max, I would not go with the 37-622 Schwalbe tire (tyre) as it might ultimately inflate up to as much as 40mm wide, and even if it maxed out at 37mm wide, a wheel that is even minutely out of true will rub.
I cannot speak for other manufacturers, they may have a different methodology for publishing tire measurements, so take my words with a grain of salt in that regard.
As for the Marathon Supreme tires, they are fantastic in terms of grip and rolling resistance. Schwalbe once made this tire in some sizes with a wire bead that made it reasonably affordable. In looking at the catalog, the wire bead version is no longer produced. It's possible that there may be some out there on the interwebs.... would be worth searching out if a grippy, fast touring tires is what you're looking for.
I hope I've helped in some way, if my post is redundant, my apologies but I started getting dizzy reading the thread.
Cheers