Yes, sorry, I do assume they are using that method. However, they have also shown a history of using up the old stock before new. This is very common in the industry and invariably since the VIN numbers are not quite in sequential order, there are some unfortunate surprises.
If Tesla is the only parts supplier, that may work ok, but someday they will probably have enough Model Ss and Xs produced to receive support from the normal aftermarket channels. (Parts stores, etc)
None of this is insurmountable. But understand that these kinds of issues are WHY other OEMs use model years to coordinate changes. It might be manageable when tesla only had one model, and was in a process of near constant minor redesign to fix initial issues. But someday soon, they will adopt the normal practice because there are very valid reasons for it. This is just one example.
