As a workaround, you can use the object I made some time ago, in the depository->01 general->graphic symbols-> Multi-Group-Sequential-numberer.
Made it after working on a six-level-parking building with 600+ parking spaces. Not that many, but when the client wants them numbered from 1 to 600+ and the layout keeps changing, numbering can take quite a time, even using the parking objects from the library.
Check it out. Just place it and drag the hotspots. Adjust the number of parking groups you need to number and then all you need to do is adjust points. Since it can show the total number of spaces per object, you can drag that text and place it in the zone stamp. It won't be part of the zone stamp, but it will update if you adjust the object.
Hope it helps with your problem.