Winchester model 70's actually started a quality decline in the mid-50's. By 1963 Winchester decided they couldn't continue to make the 70 the same way, produce a quality gun and still sell it at a profit. The gun went through a major re-design. It was so far different from the older gun that it should have been given a new model designation. Pre-64 model 70's are truly a different rifle that used to bring premium. For a variety of reasons most pre-64 model 70's no longer bring the premium they used to bring.
The model 94 did not suffer the same design changes in 1964. Quality did decline on them, but it was more gradual. A 94 made during the mid to late 60's is very little different than a pre-64. But because 1964 is the date stuck in the minds of shooters they bring a little less money.
By the 1970's right up to the end of production in 2006 were the questionable years for 94's. There seems to be no pattern that I can figure out. Some of these guns are garbage, others are as good as any ever made. Winchester quality was up and down and all over the place back then.