DVI-D cable from Monoprice missing DDC clock pin

[peoplemover]

Hello,
  I'm trying to cobble together a DVI connector for an old 17 inch Apple Cinema Display, currently with an ADC cable attached.  I don't know a ton about how DVI works, but from what I can tell, the DDC clock pin (pin 6) is used for plug-and-play monitor support.  And from other people working on this same project, it also seems to be moderately critical for doing this particular hack.

  So, I purchased a dual link DVI-D cable from Monoprice.com, cut it in half, and started stripping wires.  I discovered that pin 6 was not connected in this DVI-D cable.  This seems really weird to me, and I can't find any documentation on any site that would indicate what pins are connected in any given cable.  Granted I only paid like $3 for it, so I can't be real surprised.

  I guess my question is, the DDC clock pin, is it really an optional thing?  And if you're purchasing a DVI cable, how on earth would you ever find out what pins are hooked up?  I have had some odd results buying other things from Monoprice (a mini displayport to HDMI adapter for one), and now I've got to imagine it too was missing some pins.