Good point. I don’t actually know. But from the context I would guess that Block II refers to a revised design. Lot 2 and Lot 3 probably refer to purchase groups.
I flew the Cobra Gunship in Vietnam and had some experiences with Chinooks that are memorable. A blade failure on the rear rotor totally dismembered a Ch-47 at 1000 AGL with a death toll of 35 GI’s. Ironically they were enroute to Vung Tau for a rest period. The other entailed a Chinook that had a squealing hanger bearing in the overhead drive shaft tunnel. This is serious as the multi shaft drive, powers the rear rotor transmission. That bird landed right in the middle of a firefight and it was an exciting day to recover that crew. Both required aerial gun cover for body retrieval and perimeter security which we did with the Cobra and Little Bird.
I swore I’d never fly one as pilot nor as passenger. Several years later I was recruited to join a National Guard Chinook Unit in Stockton Ca. They sent me to school for a month and soon thereafter I checked out as PIC. I went from a fighter to a transport and man… did I get to love that big bird. Never say never, and I still get a warm feeling when I see them flying overhead near where I live not far from Ft. Carson. Aviators now flying the Chinook weren’t even born at the time I recall. Same goes for the B-52.