Different states adopt different versions of ASHRAE 62.1.
To get a better answer, more information please.
My simplistic incomplete answer is:
1-ASHRAE 62.1-2004/2007 have both people and s.f. components built into the ventilation rate procedure.
2-ASHRAE 62.1-1989 (which IMC 2000, 2003, and 2006 is based on) ventilation rate procedure uses per person only for most types of occupancies.