The voids dont count towards GFA or NLA so I would expect to see a higher area in the reference design if they are saying the voids are not built in.  But it sounds like they think the reference design is to build the floors and the dig huge voids in them which doesnt sound very plausible to me.
Its good to see collaboration with the actual tenants.  Its very common for parts of a fit-out to be included in base build only for a tennant to come in and rip them all out. It sounds unlikely though that a tennant would demolish entire parts of the floor to create a void though??
Cheers, Pat