My notes obviously don't trump the Vought Tech Manual, but the record I have shows that the single-piece canopy reportedly began with F4U-1D BuNo.57583. I know that single-piece canopied F4U-1D's in the 57xxx range went aboard the USS Bunker Hill during January 1945 for their Pacific combat cruise (the earliest I have documented on board being 57585), and that particular aircraft left the production line on July 30, 1944.
As an example, Roger Hedrick of "Jolly Rogers" fame was flying F4U-1D BuNo.57803 with VMF-221 aboard the USS Bunker Hill when he scored his final kills, and other than four months of 'pool' storage in San Diego, VMF-221 was the plane's first active assignment. I imagine the fresh planes in storage could have received post-factory retrofits before being earmarked for frontline combat but then I discovered this...
BuNo.92064 (as noted in the Vought Tech Manual) would have rolled off the line within a day of BuNo.92081, which records show was accepted by the US Navy on May 16, 1945. Single-piece canopied Corsairs had been embroiled in combat for months prior to that date, so I suppose the mystery continues?
PS - I just checked out some old photos of Bob Odegaard's F4U-4 BuNo.81857 in the condition it was in after being exhumed in the late 1970's. It has the early windscreen installed!

_________________
Rob Mears
'Surviving Corsairs' Historian
robcmears@yahoo.comhttp://www.robmears.com