You can't, with any precision, identify "model year" as we know it for classic cars. These were virtually all coachbuilt cars, so the chassis could be made one year while the body could take anywhere from a couple of months to several years to complete.
You need the chassis number off of the ID plate on the firewall/bulkhead of the car in order to learn anything definitive regarding date of manufacture. The RREC has the construction and testing for virtually all of the cars Crewe built. You can look at this webpage and purchase same if you want a really detailed history of the earliest days of any given chassis.