Actually, having worked thru several new model starts in an assembly plant, I would be surprised if there are any customer vehicles built already. Tesla has been working thru production trials ("PT"). The first customer vehicle is called "Job 1" - (Ford's claim that "Quality is Job 1" to the contrary). This will be built with some fanfare, and often becomes a museum car where all the team members have signed it (in magic marker, right on the paint). PT vehicles are required to be scrapped both for tax and insurance reasons. (Many having already been consumed by crash testing).
In summary, if Tesla has already built any vehicles destined for sale, it would mean that Job 1 has already occurred and production is in progress. (That doesn't necessarily mean production at the final TAKT time; sometimes a conveyor line is run slowly for a few weeks until all team members are up to speed on all standard procedures). See book "Toyota Production System," Yashiro Monden, 2011.