Folks call everything a VIN, as if it were just another name for a serial number, a kind of shorthand or nickname. I understand the tendancy. But the two things are completely different, to those who know the difference, which I admit isn't everyone. But bear with me.
A serial number and a VIN are very different animals. Until January 1981, manufacturers weren't actually required to even have an identifying number on its vehicles (nor, incidentally, are manufacturers required to have warranties, even today). Having a serial number, and here we mean an identifying marking on the vehicle's frame) was completely voluntary. But of course all manufacturers had them because it was useful for their own internal record-keeping purposes. However, as you might expect, every manufacturer had their own proprietary serial number system. They could do with it whatever they wanted, code it as they wished, and change it or reinterpret it any way they chose to. Remember, no one told them they had to have one. And of course, this meant no two manufacturer's serial number systems were alike, not to mention that even year to year within a single manufacturer's system there was a lack of consistency. This was the situation with serial numbers. They really meant only what the manufacturer intended, with no outside oversight, and no consideration for communication outside the manufacturer's offices. Secret codes with meanings, if you will, if any, in other words. And, wouldn't you know it, the manufacturer could reuse the same exact markings as many times and as often as they wanted. And some of them did. For more on that particular issue, watch for my upcoming article on the 1975 change in model designations.
Serial numbers reigned until 1981, when everything changed. A few years before, late in 1979, US lawmakers wrote a new Federal Motor Vehicle Safety Standard (FMVSS 571.115) in which it was proposed that from the 81 model year forward (giving manufacturers ample time to comply) frame markings would, by law, actually mean something communicable and trackable. They would identify the vehicle, include engine size and power codes for the benefit of markets such as Japan and Europe where licensing and taxing was based on these, and very importantly, communicate the model year, exact model/body style, the manufacturer's plant, and so on, all for the expressly stated and very real and vital purpose of increasing the number of vehicles successfully recovered and repaired in the all-important and unfortunately rather frequent eventuality of manufacturer vehicle safety recalls. The highest purpose of all. The VIN's reason for being. Up to then, recalls had a much lower completion rate. That is, many more slipped through the cracks. Even today, saturation is never 100 percent. But before VINs, it wasn't even close.
And the VIN brought three other really interesting new things. One, unlike the situation with a serial number, which the manufacturer could repeat whenever they wanted, each VIN had to be absolutely unique for a period of 30 years. That's right, no two VINs could be indentical for a 30-year span, after which a VIN could be repeated (and as of this writing already has). The other significant and actually related new thing, and the most important from a law enforcement perspective, each VIN included an anti-theft code that if altered red-flagged a stolen vehicle. Unfortunately, the anti-theft code has at this late date long been available on the Internet, so that part is a bit of a fail. Chalk it up to the online explosion of information. Third, the VIN, through its model id portion, easily communicates the vehicle as either on-road or off-road. Presumably state motor vehicle divisions would be using this, and most are, though inexplicably, some of them are to date ignoring it and blithely licensing non-DOT and non-EPA legal vehicles for street use, and even worse, not always sharing the fact of this peculiar exemption to their own state's law enforcement agencies. Go figure.
As mentioned, unlike a serial number, this VIN system would be consistent across all manufacturers, because though originating in the US and applying only to street-going vehicles sold in the US, since no manufacturer wanted to be left out of the US market, they all complied, making it worldwide. And since manufacturers avoid expensive single-market assembly lines, even non-US market vehicles received VINs. This is where we are today. In many ways, the VIN could be called the vehicle's DNA. Exclusively unique, traceable, and superlatively informative.
So, to recap, a frame number on a street-legal vehicle marked as a 1980 or earlier model communicates at best only production sequence, i.e. "serial" information, which is why it's called a serial number. A VIN by contrast records not only serial information but much more, by means of its mandatory sections revealing everything but what the assembly line worker had for lunch. Thus, calling a serial number a VIN is technically uber-incorrect and in a practical sense misleading, since a serial number, if it conveys much that is useful at all, is of no informational benefit to the public, but only to the manufacturer. A VIN is full of information vastly more useful to both parties, plus insurance companies, lawyers, and governmental agencies.
By the way, speaking of insurance companies, the government and DNA, wait til you hear about the "flight recorders" manufacturers are putting on motorcycles, and have been for several years. But that's another article.