What's the point of "9", then? And how do you explain DE15 (popularized by VGA)?

> What's the point of "9", then?

Originally? Because that was the naming convention that Cannon designated. Later, because the shell size wasn't sufficient to determine the number of pins.

> And how do you explain DE15 (popularized by VGA)?

Cannon's D-series connectors started with 2 rows, at the "normal density" of 326/3000 of an inch between pins. They later expanded the range of connectors with "high density" and "double density" connectors that put more pins at greater densities into the original shell sizes. DE15 is in the "high density" range.