Con-Cor
Con-Cor produced a line of 1:87 HO scale Blue Bird body on International chasis school buses in a number of variations. The boxes read "Manufactured in Cooperation with herpa models of West Germany". Con-Cor buses represent a unique sector in HO scale layouts as there are few other school buses in that scale.
It appears that some item numbers have multiple variations. In particular certain models of the yellow school bus can be found with a white roof. These white roof variations also feature brown seats instead of the green of the yellow topped buses. In addition the white top variations appear to be more scarce. It is unclear whether or not all models had both white top and yellow top variations. I might speculate that the white top models are a later production run. Possibly intended to be representative of a later time frame like the 1990's, whereas the green seats are more suited for 1980s layouts.
Con-Cor No. 0004-001035
Model: Blank

Above: white top & brown seat variation. Below: yellow top & green seat variation.
Con-Cor No. 0004-001036
Model: County School District 4
Con-Cor No. 0004-001037
Model: Unified School Dist. #2
Con-Cor No. 0004-001038
Model: Helping Hands Temporary Labor
Con-Cor No. 0004-001039
Model: Maintenance of Way X317
It appears that number 0004-001040 and 0004-001041 were not item numbers used by Con-Cor. Item 0004-001042 is an Atlas Van Lines semi-tractor trailer, numbering then returns to buses.
Con-Cor No. 0004-001043
Model: U.S. Army Transport
Con-Cor No. 0004-001044
Model: Camp Woebegon
Con-Cor No. 0004-001045
Model: Washington High School
Con-Cor No. 0004-001046
Model: Good Shepherd Church
Con-Cor No. Special Order
Model: Grand Rapids Public Schools