If it isn't on Wikipedia, then it certainly isn't very well known, especially for computing terms.
I sincerely hope you don't actually believe that Wikipedia is a valid source by itself.
Wikipedia (and the Internet) didn't even exist very long ago. Wikipedia has relatively little of the world's knowledge, and what it does have, often has few or bad references. Anything related to the iPhone is usually most suspect of all, due to fan submitted material.
Also bear in mind that just because we didn't know a term until recently, that doesn't mean it hasn't been widely used within its field for years. For instance, I started programming for capacitive touchscreens almost twenty years ago. It was a well known term in the field. Most of the public only heard of "capacitive" a few years ago.
I really can't find any official documentation of multitouch before 2006 (e.g. publications).
Learn to search books, papers, etc. For example:
1. Go to Google. Enter "multi-touch" with the hyphen. This allows it to search for both with and without it. Click "Google Search".
2. When you get the first results, click on "More" at the top and choose "Scholar". One of the first few results is from 1985.
You can also search magazines like Time, Popular Science, etc for articles. This is especially fruitful for terms involving consumer items such as "touch tablet" or older terms that were widespread a decade ago. (The first result in PopSci for "
webpad" is for a 1999 touch tablet running on QNX ! )