The Kalamazoo Secondary hosted two pairs of trains to Grand Rapids into the early 80s after traffic from the GR&I was rerouted through Elkhart. One pair to Chicago and one pair only to Elkhart. A duplicate route was made available between Kalamazoo and Three Rivers by using the Air Line and GR&I through the PC era. The diamond and switch for the east end of the siding at Wasepi were removed and the siding tied into the GR&I going north. Prior to that there was EK1/KE2 operating between Kalamazoo and Elkhart, which was the only road train south of Kalamazoo. I imagine this was discontinued when they began operating IGT/GTI between Elkhart and Jackson via Kalamazoo. During the PC era TV16 ran from Kalamazoo Mosel Yd to the east coast, and less frequently TV15 in the opposite routing. After through traffic was removed from the Air Line, the passing siding was put in just north of Three Rivers and through traffic to points east of Jackson began running north to Kalamazoo and east on the Michigan Line. For a short while around 1982 Conrail ran KZLA/LAKZ between Kalamazoo and Lansing shuttling autoparts.
After the original Air Line portion of the Elkhart Branch was downgraded/CTC deactivated, the portion of the Elkhart Branch from Elkhart to Three Rivers became the Kalamazoo Branch, the former Air Line between Three Rivers and Wasepi (along with the GR&I from Wasepi to Mendon) became the Mendon Secondary, and Wasepi to Jackson became the Wasepi Secondary.
I don't think it was until the late 80s/early 90s that Conrail settled on the three pairs of road trains operating east of Kalamazoo. Based mostly on train movement sheets I have, in the 80s it seems the road trains were run less regularly/frequently than in the 90s, although INGT was daily and often had an extra section.
You can find a lot of info on train symbols, scheduling, and traffic routing on the Conrail freight schedules on multimodalways:
http://multimodalways.org/archives/rrs/CR/CR%20Freight%20Schedules/CR%20Freight%20Schedules.html