I'm not sure, but does the rear "drum" have a adjustment on the cable to adjust as the shoes wear?
Yes.
Look right down where the cable pulls a lever at the rear wheel. On my Piaggio it is on the left side ...cable runs under the belt cover.
You'll see that you can effectively shorten/tighten the pull of the cable by tightening a nut there (hex nut or thumb or wing nut)
Drum brakes reportedly last a long time. Adjust at the rear by drum, with less than 1/2 " of pull on the lever.
Owner's manual doesn't illustrate this??
Stig