I believe you already know this but I'm going to take a stab at a different explanation.
I think what you are measuring in the print is a 7 stop change in refletivity from black to white. That's not 7 zones.
Zones do not equal stops in a print.
The print always has all 11 zones regardless of the luminance difference between black and white.
In the print you measured; "7 stops = 11 zones". That means that each "print zone" is only 7/11ths of a stop wide on that print.
In the field we may have a scene that from black to white is actually 13 stops wide, 2 stops wider than the normal 11. In that case each zone in the scene is 13/11ths of a stop wide. We could also have a scene that is 9 stops from back to white, the scene zones would be 9/11ths of a stop wide in that case.
The magic of the zone system is that if you have 11 subjects in the scene that you want and they are evenly spaced running from white to black, and our development and printing are done properly those same subjects will print perfectly from black to white on paper. 11 zones in the scene = 11 zones in the print regardless of how many stops are measured in the scene or across the print.
Side Note, which will not add any clarity, the math here isn't perfect, though I believe thinking about it this way is reasonable and it is how the zones are illustrated normally, all 11 zones being equal in width. The real width of 11 zones; could actually be 9 plus pure black and white. Zones zero and ten may not have any "width" in the real world, they may simply be points at which the the tone starts.