Occupancy Counts differ from workstation count significantly

I'm working on a 800,000 s.f. high rise building with 40 tenants. The building manager knows that there are 1,500 occupants because everyone that works there must have a key card to get into the elevator. The building manager is not aware of which workstations within each of the suites is vacant. They After imputing information for the 2,008 offices and workstations in the building the reviewer is justifiably asking about the wide variation in occupants (1,500) and office workstations (2,008). Going through each of the suites to try and determine which of the 500 or so work areas is vacant is not realistic. It would require walking through the building during the day and some tenants would likely not allow that. Our lighting control for all space types is very high. Randomly removing some of the workstations and a few offices would not affect our ability to meet this point. What should I do? Thank you in advance for your help.