I have a JD 550-C that I’m trying to fetch the year from serial number 550-C 335027T
Mid to late 70's. That machine is a straight 550, not a 550C. The "C" in the serial indicates an inside dozer frame. Also, a specific year cannot be determined on the older serial number format. If you are looking for parts, years don't matter anyway. Serial number is king in this industry.