My IR experience goes back to the early 90’s and never in my life have I seen a three conductor emitter.

With Xantech, you could buy a standard emitter or a visible emitter, with no difference at the plug. Supposing there were three conductor plugs, what would they connect to? A 789–44 connecting block didn’t have two and three conductor jacks, nor did URC, RTI, or any other IR base station/extender systems I can think of. RTI had multi-conductor jacks on the RP-6 processor for their proprietary dongles, but included 4” long adapter to make them 2-conductor emitter friendly.

I have some old emitters in my truck, including some single plug dual emitter options, and a twin-plug single emitter to connect to two separate control  systems at once, but nothing in three conductor.

Electrically speaking, there is no need for a third conductor as the emitter for the equipment and the visible LED can simply be paralleled.

I think your memory might be getting a little foggy lol