To forecast how many sales people will be needed using a sales force people$-$forecast model,:

any upcoming hirings, promotions, and transfers in must be subtracted from current sales force personnel

all employee hirings, promotions and transfers in must be added to all forecasted employee quits, terminations, promotions, transfers out, and retirements; this sum must be subtracted from the number of current employees

employee quits, terminations, promotions, transfers out, and retirements must be ignored

future sales force personnel are forecasted by looking at operational objectives

the current number in the sales force must be added to the upcoming hirings, promotions, and transfers in; quits, terminations, promotions, transfers out and retirements must be subtracted from that sum