It is my understanding, that the model years designation was not required until 1982, when the current 17 digit VIN # was required by the feds. At that time, and still, the 10th digit is the designation for the year model. Each decade <span style="font-weight: bold">can</span> bring a new system, for example a 2011 has a "B" for the year code, and 2010 had an "A". The rest of the word has generally followed our 17 digit VIN #, but all have not used the same code for each digit.
Also, it appears that the British car industry was on a different planet from the American car industry.Duh
The American car industry was very resistant to making changes in mid year, and mid model, unless absolutely necessary, while the Brits made on-going changes, regardless of the year, or time of year. Most of the Brit cars were improved and modified during the model build to "improve the breed" and hence the problem of knowing what part was in what car, except by the tracking of the vehicle #.
Cheers,
Scott in CA