Forum:Unknown tasks

I have been playing online on mw2 for some time now and have endeavored to complete all the tasks in order to get all emblems associated with the tasks, however recently while I've been playing I've been give awards for 2 tasks that are not mentioned and have not received any emblems for them, 1 was will 3 enemies in 1 life with 3 different weapons and the other was injure an enemy them knife him in the back. Are there anymore hidden tasks out there?

Any advice would be appreciated.