The glove box light was included as part of the RPO Z87 Custom Interior; without the Custom Interior, you had to order the ZJ9 Auxiliary Lighting Group to get it (that group also included an ashtray light, courtesy lights, underhood light, and trunk light on coupes - courtesy lights were standard on convertibles).
My '69 has the Custom Interior (with the glove box light), but doesn't have ZJ9, so it doesn't have the other lights.