By
DMX, you mean the old Canon style connectors? (
XLR)
As far as I know, DMX is only in 5 and 3 pin styles, but the Switchcraft / Canon / Neutrik connectors come in many configurations. 7 pins might be handy for 6
channel analog dimmers among other things. (6 chns & common, so you don't use the shell.) So, maybe they have been there for awhile.