There was a change designation in 1967 for the Canadian plants. Up through 1966, Oshawa was 0 and they built full size cars, Novas and Chevelles. (St Therese wasn't yet in production.) Starting in 1967, they changed Oshawa from 0 to 1 and added St Therese as 2.
This information came from my September, 1968 P&A 25 (1969 Chevrolet Illustrations and Special Information manual) under the Assembly plant designation section.
Ed