@IslandHydro You may have already seen this site, but it’s a list of all the changes to the Model S over the months. Like it was mentioned above, Tesla rolls out changes as they become available so you really have to look at the build month. For example, if you wanted the enhanced anti-theft add-on system, it’s only available for September 2015+ builds. Another example is I think at some point in 2015 is when they started rolling out LTE instead of 3G for the cellular connectivity (don’t quote me on that), although a lot of folks probably upgraded.
I picked up a CPO about a month ago and my criteria was a late 2015 85D. I was contemplating the P85D but ultimately decided the 85D had more than enough performance and a slightly increased range (I believe ~17 miles) at a much cheaper price. I’m sure you you’ve already seen the threads about the CPO process being pretty terrible, but I also wrote a fairly detailed on my experience here. Anyways, best of luck finding what you want! They are awesome cars and I can’t see myself going back to a gasoline/diesel vehicle (except for maybe a truck to tow).
I had seen that site, but thanks for reminding me. I think I might try to start tracking build date (as apposed to build year). It's not exposed on CPO-Hunter, but you can often get it from the pictures. I'm super excited about getting an S, a few months away yet, as were giving our son one of our cars for a graduation present, and the S will replace that car. Plenty of time for me to really zero in on what car is best for my preferences / budget.