IMO, the issue is less that there is a shell designation and more that the shell designation is hard to interpret.

A single letter doesn't have a lot of meaning on its own, and the A-E order is not consistent with the E shell being smaller than all the others.

By making it fully adjacent to the 'D', it makes the letter sound like it's part of the standard's name, like the 'RJ' in 'RJ45'.

It would have been better to focus on pin count and row count, as those along with standard pin spacing drive the shell size.

D-2R-15 for a two row 15 pin connector equivalent to DA-15, D-3R-15 for a 3 row 15 pin equivalent to DE-15 / VGA.

Could trim out the 'R' and go with "D2-15" for 2 row and "D3-15" for 3 row, if brevity is preferred.