I have '04 G35 6MT with Aero, Nav, and Sport Pkg (Sport is standard on 6MT), all factory installed - never was a rear parcel shelf brake light, nor a place to mount one.

Dealer installed rear spoilers will have the rear window light, unless they replace the package shelf (the whole shelf itself is called the "rear parcel shelf finisher", and how it is "finished" is dependent upon what you have).

For example, the "finisher" is different for the standard shelf with integrated stoplight, as opposed to standard shelf without stoplight (meaning the light is on a spoiler), as opposed to shelf with Bose stereo speakers and subwoofer with stoplight, as opposed to shelf with Bose and no stoplight, etc., etc.

Dealer parts guy is a clown, and shouldn't be working in a job where he has no interest in learning his product (welcome to America, land of the apathetic worker).....

DB