Yep I have noticed some places will spot replace with LEDs if the old HID cobrahead fails. And uh David, one of them is an OVX...not 2 OVMs....but one OVX and one OVM....but all of them are C-Hinds....except of course the LED...
I'm guessing Boston originally had a dimming system when these poles were installed. It makes sense if both lights came on at dusk then at 11PM or midnight or whatever one of them would shut off to lower the brightness/save energy instead of using one 700W MV lamp all night, two 400W MV fixtures were used. Just a guess, as i know some places have done that (RI not ones of them LOL)