differential shims

well most new gear sets come with shims just to be safe i would get some new ones they are pretty cheap make shure you put a new crush sleeve in their as well if you bought them new that shold have been in the set with gears as well just my 2 cents didnt really answer your question just get new shims better safe then sorry
 
You really need to set the backlash correctly just in case, but you need the tool for that.

A mech. did mine so I don't know what amount of shims were where. the one you're talking about probably came from the right side.