The intro says "One year ago" and shows Sam/Lucifer jumping into the hole with Adam/Michael. Then it says "Now" and Dean wakes up with Lisa in bed. Swan Song actually was only 4 months before Exile On Main St, not a whole year.
Sam cuts himself with a knife to prove to Dean he is not a Shapeshifter, as they are burned when touched with silver. However Sam is using a store bought common pocket knife (looks like a Geber), which would not have a silver blade.