Have been involved in a bit of a non-debate (as in the other side doesn't want to explain their position) on whether traders can just rely on data from COMEX. My answer is no, as the COMEX precious metal markets are but one part of the total market for paper and physical metal and through arbitrage are tightly linked to each other. Therefore just relying on COMEX open interest, volume, etc data will give one an incomplete view and thus trading methods based only on COMEX analysis will produce a lot of "surprise" events/patterns.
I covered this point in this post on short term trading. To observe me banging my head against a brick wall, and for a further exposition of this view, read the comments posted at Scott Pluschau's blog.