As I said, I think both programs were delayed, not by technical problems, but by the availability of cash due to higher priority programs absorbing all the company's available money.
Bingo. Progress on the 609 was slow because Bell basically decided it wasnt marketable at its current gross weight, and they were probably looking at ways to get out as "financially gracefully" as possible. I wouldnt be surprised to see them sit back and watch what happens with the 609 in Europe with certification and possibly re-enter the civil tiltrotor game with a model that would actually sell.
If you ever read about how difficult certification can be, especially with a new type of flying vehicle, you might appreciate a lengthy development period.
And actually, the 76D has new blades, engines, and fairings (among other misc things). The rotor system is basically the same.