Ok, traders there is some genuine controversy going around on a couple of items. Let's address them one by one.
Genuine Purity Fist: Apparently there are several (at least) hoarders of this item. They have many of them in their respective backpacks. Facepunch has the story here. There were several SPUF threads however most have been deleted (not closed, per usual) by moderators. Strange but conspiracy theorists we are not. There remains a semi-informative SPUF thread here. The bottom line: don't buy a genuine purity fist right now. If you do, buy it on the cheap only.
Clean Spine-Chilling Skull 2011: As with Spine-Chilling Skull 2010, there is another "glitch" that made some of the 2011 versions craftable (note: the 2010 glitch made some of that year's version tradeable). This is verified in the official wiki here. The bottom line: this does appear to be a rarer item and a price-clarification is coming on both clean/dirty versions. However, there appear to be many for sale right now at values all-over-the-map. Until the market sorts out, we will watch and see.