Required to use Actual Occupant Density?

Actual occupancies have never been required when the ASHRAE defaults are higher makes no sense. The LEED Reviewers as passing on a new required compliance rule developed by the USGBC's LEED Department. The USGBC is essentially demanding that a mechanical engineer prove compliance with ASHRAE 62.1 for a building that may well be under-populated, at least when a LEED review is occurring. From the ASHRAE 62.1-2007 Users Manual, Example 6-D--Planning for Future Revisions: "...the design zone population can be based on expected occupant density, not on a future possibility. However, even though it is not required, anticipating future needs may still be a good idea. It is common for designers to include safety factors in HVAC designs, in part to handle unexpected revisions and space usages that increase loads. If overcrowding of the classrooms is a likely possibility, designing ventilation and HVAC systems for the added loads can obviate the need for expensive future retrofits."

I have been researching this actual vs. default occupant density issue for a project I am working on. ASHRAE 62.1-2007 states on page 11 of 6.2.2.1 for Breathing Zone Outdoor Airflow: “Pz - Zone Population: the largest number of people expected to occupy the zone during typical usage. If Pz cannot be accurately predicted during design, it shall be an estimated value based on the zone floor area and the default occupant density listed in Table 6-1.” ASHRAE 62.1-2007 User’s Manual states on page 6-14 under Estimate the Number of Occupants in the Zone (Pz): “The default occupant densities listed in Table 6-1 are based on past experience and judgment. The Standard requires that if the number of occupants is not known (i.e., if none of the above information is available) then the Table 6-1 default densities must be used to calculate the number of occupants in a given space. However, these values are not mandatory when better information is available.” See page 6-14 of the User’s Manual for details on the "above information" which includes using the Program, Furniture Plans, and Industry Data. Note: ASHRAE 62.1-2007 User’s Manual is a free resource under Credit Resources in LOv3 and in the Credit Library on USGBC’s sites (under Resources for EQp1) as 62_1_2007_UM.pdf. I read this as using actual occupant density is the way to go if you have the information.