Mark,
I don't believe that # 13 can be extended any further.
I think the new back tee, built when ANGC acquired land from ACC, is about at the property line.
While ANGC has historically been tweaked, dating back to its inception, I don't know that tweaking occured every year, although it might have.
As to building new sets of tees, I don't see that happening.
I think ANGC will preserve its two set configuration, Members and Masters.