Could also be done to boost 4Q19 sales numbers...Imagine that Tesla was getting requests from customers to hold deliveries until they could get a 2020. Decided to label their current production to be 2020's, as not to get any possible EOY deliveries pushed out to next year.
Could also be done to assure that cars in shippment overseas, and scheduled for delivery some time out, get the 2020 dating.
This while model year thing has to be a gigantic hassle for Tesla. They would much rather their cars be dated the date of manufacture. Would be much more clear for everyone.