> Is there some landmark "first commercial use" of the classic T1-3/4 > individual LED package that's so common today? Were there early > LED packages that just completely disappeared?

I've used LEDs on what seemed to be a TO18 header (like a 2N2222 transistor) with an epoxy top. I've also seen an LED (the number MiLED 500 springs to mind) in a clear TO92 package. Neither are common today.