Yuck I have
some of these, either miniDin9 or close on one end, looks like
RJ11 on the other (hoped they were serial cables for Seiko label printers),
but clearly marked DECconnect Office Cable. Rats.
DECconnect Office Cable is just what it says -- a cable. A flat, 6 wire
cable IIRC. You could buy a reel of it from DEC and use it how you liked
-- not necessarily for linking up DEC machines.
So your cables could have been designed for just about anything.
Finding the pinout of the Seiko label printers was the hard part. I kept
buying the printers without cables, thinking "soon" I will find the pinout
on the net or find a cable to check, but it took many months (pretty sure I
have it now).