There also existed non-standard D-subminiature connectors that didn't fit within that nomenclature.

For instance, the Amiga used 23-pin connectors to connect displays and disk drives. They had the same pin spacing as DB25 but were slightly smaller.

And there's the infamous DB-19: https://www.bigmessowires.com/2025/06/30/bulk-lots-of-db-19s...

Wouldn't it fit into the nomenclature with another shell type? DF, perhaps?

It is not like there is any real sensibility to the naming anyway. Of the common types, DA, DB, and DC seem to follow a pattern, but DD and DE then go completely off the rails.