DRXOLDS

Maybe a little out of context.....but why are most '71-72's with rear window defogger, controls missing the light (assembly bolts to same bolts as defogger switch with about 3/32" hole for light) that illuminates the little red dot when on?
I own 2 (control set-ups for cars with A/C, they both have the complete set-up with bulb) and I am curious......why most are missing and forget about finding them....
Thanks in advance!
DRXOLDS