Inspired by this question, I recall that many of the older Microsoft products from Windows 3.1 through the late 90's / early '00s supported a 'test' activation code of all 1's. I did this a few times out of laziness on Windows 95/98 machines many years ago.
In other words, if you installed Visual Basic 4 you would have had a certificate of authenticity with the product that contained a code you would enter to complete installation. However, it was possible to punch in simply all 1's to get things to work.
I believe all this changed in the early 2000s when Windows XP came out most likely due to the Microsoft activation service probably being made available by the OS. But that being said, was this '1s trick' possible with all their products until a particular year? Did it cover everything or just some types of product? Of course, perhaps it is possible that 1's wasn't intentional but just happened to satisfy whatever algorithm was being used!
*NOTE: I haven't done it in years, but I think it was 1's.. might have been something else!