From what I know the 250X was offered in 1969 and 1970. In 1971 the model name was changed to R2501 as with alot of other model names being changed. The Hustler model was introduced first in 1971. (biggest year for new models) The Duster is not a Cat. It was made by the same manufacturer "HPE / Muskin" to be sold in the Penney's line of mini bikes along with the Duster MX. The Duster was introduced as a 1970 model but is shown in some literature from 1969. HPE / Muskin used serial numbers, but not even a previous owner who bought Muskins inventory knows how you would go about deciphering them.