The real reason is that in the 1980s this illustration ( https://cdn.sparkfun.com/assets/home_page_posts/1/4/2/9/8/DS... ) was not shown to people. And an illustrator, probably who hadn't seen it either, is who got it wrong. I don't blame them. The existence of an arbitrary letter invariably joined with a useful and descriptive number is the fault here. And the illustrator could NOT show the whole thing anyway because it contained diagrams of products not sold. The perfect setup.

That is all. Everything else is blah blah blah (about DB9, love all the examples of other goofy identifiers!)

People strive for accuracy and remember things. I love people-in-general and they have an impressive track record. They improved on the standards committee.