Jeff Suppan is the only pitcher in my data who made 400 or more starts, but was never designated as a #1 starter.   Ten pitchers had 300 or more without ever moving to the top of the rotation:  Suppan, Jim Slaton, Todd Stottlemyre, Terry Mulholland, Dick Ruthven, Ray Sadecki, Woodie Fryman, Jason Marquis, Ray Burris, and Sad Sam Jones.  Jones, the guy from the 1920s, made 400+ starts, but many of them are not within my data.