Containers might also be another thing to look at they were introduced in 2010, aparently they are a step up from XRef. havent tested them myself much. It seems you save each object into a container file and load instances of it into the scene, saving over the container updates every instance of it.
I would stay away from xrefs, I've had nothing but trouble with them. The most common issue I ran into was that they would lose the link and stop updating if I made changes to the original. I would then have to click on each one and load each xref. The problem with that was that I had hundreds, and when the link broke the…