Watsonian sidecar body numbers can usually be found on a brass plate located beneath the seat or, on the wooden dashboard (if the model has one). It is possible to identify the year by the letter prefix as follows:
|1950-59||A/50, B/51, C/52, D/53, E/54, F/55, G/56, H/57, K/58, L/59|
|1960-69||M/60, N/61, P/62, Q/63, R/64, S/65,T/66, U/67, V/68, W/69|
|1970-79||X/70, Y/71, Z/72, A/73, B/74, C/75, D/76, E/77, F/78, G/79|
|1980-89||H/80, J/81, K/82, L/83, M/84, N85, P/86, R/87, S/88, T/89|
|1990-93||U/90, V/91, W/92, X/93|
Model numbers start with A in 1950 and run to Z in 1972, starting again at A in 1972 ad continuing to X in 1993, when Watsonian ceased to number bodies.
If you are trying to identify a specific model classic or vintage sidecar, you may find it in this selection of Watsonian sidecar brochures, which also includes some Squire sidecars.