The tylenol is optional. Typically you'll see it written as oxycodone 15mg/7.5 ... the second set of numbers it the accetametaphine ... which is basically an anti-inflamatory; ie tylenol.
With long term use of the narcotic with the antiinflamatory, and all the concerns lately about long term use vs effect of the anti-inflamatory, when they renewed my percoset perscription (which is what I take four times a day) my doctor simply removed the anti-inflamatory as it didn't prove to be giving me any added bennefit. The reason it's normally included is simple .... usually when there's pain, there's swelling, but when you're dealing with a CRPS patient it's our nerves that are affected and faulty, so swelling is usually a side effect of something else.