Pdp 11/20 front panels

I own an early 11/20, sn300, also of the PDP-11 only markings, like the unit in question. My front panel PCB is date stamped 1970, and it is the led type. I also have original DEC schematics that show first bulbs, and then a revision to allow bulbs or LEDs. I also have some other front panel PCBs with bulbs. My best guess would be that they did a revision for LED's, and then perhaps dropped them due to cost or availability. So it appears that LEDs were at least installed on some 11/20s. My LED unit does not have the front panel drilled out, but I suppose they may have done that for one of the early proto types while they were trying different designs. My 11/20 was supposed to have been gotten from the dec Mill factory in Mass, perhaps the early LED units were never shipped out. So it is likely that the 11/20 for sale is for real. Chad Martin