Do keep in mind this was a DB19, and presumably the manufacturer already made other connectors in the same family; hence they had a fair idea how all of the detail not obvious from the supplied drawing would be.
Fair guess - they took a DB9 drawing and inserted additional pins using whatever CAD system they were using, then entered production.
I haven't soldered anything but DB9s in later years, but I am pretty confident both pitch and edge shape is identical on DB9, DB15 and DB19. (I have a vague recollection DB25 is slightly closer pitched, but may well be mistaken.)
That being said, one can never supply too much information to a supplier - if nothing else to be able to shrug and say 'not to spec' when some seemingly irrelevant (to them) shortcut bungles your project...
Technical correction: the proper designations are "DE-9" and either "DE-15" (if you're referring to the high-density three-row connector used for VGA) or "DA-15" (if you're referring to the original lower-density two-row 15-pin connector). The second letter referred to the shell size, so a DE-9 and DE-15 had different numbers of pins arranged in the same-sided shell. Wikipedia has a good section on this: https://en.wikipedia.org/wiki/D-subminiature#Description.2C_....
The so-called "DB-19", on the other hand, had a nonstandard shell size, so it doesn't really have a proper name under the original system. Maybe "Dx-19".
Fair guess - they took a DB9 drawing and inserted additional pins using whatever CAD system they were using, then entered production.
I haven't soldered anything but DB9s in later years, but I am pretty confident both pitch and edge shape is identical on DB9, DB15 and DB19. (I have a vague recollection DB25 is slightly closer pitched, but may well be mistaken.)
That being said, one can never supply too much information to a supplier - if nothing else to be able to shrug and say 'not to spec' when some seemingly irrelevant (to them) shortcut bungles your project...