The Rob Cook books dates as follows:9/72 badge series was in production 1972 through 1975 and was the last of the Swivo era Rogers. 1972 – Serial # underlined with no prefix1973 - letter "A" followed by serial #1974 - letter "B" followed by serial #1975 – Serial #, no underline or prefix
in the Rob Cook book there are a lot of things that are incorrect
not saying this particular info is incorrect ... but the book has plenty of mistakes