yes they do exist, my guess is that there may be two reasons.
1. they may be from the early days, when the daughterboard port standard is experimental than fully established.
2. they may be oem products only intended for corresponding soundcards. for example, i know a compaq version of ess689 daughterboard whose connector has one hole missing, thus only compatible with its own soundcards.

Yeah, both DB's along with home PC market versions has "professional" versions, related to musicians - EMU 8801 Sound Engine DB was inside EMU Sound Engine external module and AVM Summit General MIDI engine was inside Buchla Lighting II - sensor MIDI controller. Also i has that DB by Compaq with one missing pin. 😀

E-mu is more-or-less reponsible for the creation of the 26-pin MIDI daughterboard, having initially designed the EMU8801, "SoundEngine" board as an OEM product for use in any number of multimedia applications, with the earliest such product (that I'm aware of) being the "One Stop Music Shop" board for Amiga computers. Creative simply adapted the EMU8801 board into the design of the SB16, in what became known as the "Wave Blaster."

It seems reasonable that the "reversed" connector positioning was likely the original intent, despite Creative's adaptation (and that of other DB manufacturers following suit) going on to become the standard.

Here are some product announcements, if you're interested:
http://www.symphoniae.com/soundcard/Creative/ … /DOCS/E-MU1.pdf
http://www.symphoniae.com/soundcard/Creative/ … /DOCS/E-MU2.pdf