See my other article comparing the old serial number system with the current vehicle identification number (VIN) system, with an emphasis on revealing the vast differences betwen the two. In that article I revealed how wrong it is to call just any serial number a VIN. Though not such a serious gaff, it does nonetheless considerable injustice to the comparative power and usefulness of the VIN as contrasted with the serial number. They're very different. Refer back to that article to get an idea.
But the plot thickens. Even before the VIN system was created, some interesting things were happening to vehicle identification methods. Lawmakers had long been scrutinizing what was a very loose system, one that permitted manufacturers to enhance the salability of leftover models by presenting them as freshly made. Yup, post-dating unsold vehicles. Better believe it. But here's the thing: nothing prohibited this. It was not illegal. There was no control over what year a manufacturer assigned to his product. None. In fact, vehicle model years was a totally voluntary notion, and one that didn't even exist for the first 40 years of the history of the automobile. So manufacturers could morally and legally sell leftover vehicles as future models, if they could slip them past the public eye, and in low sales years with few changes from year to year, this was easy to do.
Until 1975. It was then that legislation was passed which mandated the addition of a model year to the already-existent manufactured year, to vehicle chassis markings. Two dates on each frame, in other words. Bike makers could still post-date, if they dared. But now the consumer could tell, by comparing the two stampings, just how old this "new"model really was. Kind of the motor vehicle equivalent of the use-by date on your milk carton.
But only from 1975 onward. This explains why vintage motorcycle owners are often unsure as to the model year of their pre-75 machine. It's kind of up for grabs. They resort to the many published collectors' resources that are available, including manufacturer's model identification books (the Big Four Japanese help here) and specifications lists put together by vintage enthusiasts focusing on such things as types of fasteners or lighting equipment, or taillight sizes that changed from year to year. Manufacturers often sprinkled a handful of an upcoming model's parts on the last couple hundred bikes made prior, so that can confuse. Then there's the "after September"rule. Many folks believe that if a pre-75 bike's manufacture stamping indicates September or later, then the bike is the following year's model. Often this is a pretty fair guess, because generally, manufacturers conduct meetings in October to reveal to their dealers next year's models. But it's not an infallible rule, unfortunately. For one thing, some manufacturers release new models six months apart. Another problem is the well-known tack many state registration agencies take on pre-1975 bikes, the easy way out from their point of view, of simply assigning as the model year the year the vehicle is first registered. All of these inconsistencies are very frustrating to the collector and the purist.
As mentioned, this all got straightened out for 1975 and later. Curiously, 1975 was in fact a big year for consumer legislation, bringing as it did the left side gear shift rule, headlights always on, and a host of similar vehicle laws. Among these was the watershed Magnusson-Moss Warranty Improvement Act, the most impactive piece of consumer warranty law up to that time and possibly even since, because it gave consumers a ton of newcrights, not the least of which was it made it impossible for manufacturers to "void"warranties. That's right, they can't, not since 1975, and thanks to so much of the misinformation in this industry, another thing you probably believed that isn't true. More on Magnusson-Moss later.