The Marines were aware in the late 1980s that their CH-46 fleet would realistically need replacement by 2000 or so, considering the fact that most of their airfranes dated to the 60s and 70s. When development started in the mid-1980s, the Osprwy was probably supposed to enter service in the mid-1990s. However, after the Osprey crashes in 1991 and 1992, the Marines may have considered procurement of the forthcoming EH-101 as an interim replacement for the Sea Knight. I've only seen references for this timeframe on Wikipedia, put there are other documents from the early 2000s considering replacement of some of the V-22 buy with EH-101s.
If the Marines have an interim medium-lift solution in place by 2000, how would this affect V-22 development and how could it impact Marine combat experience in Iraq and Afghanistan prior to the OTL retirement of the Sea Knights?