GM for example would add about $3k per car to gross margin if they did it the Tesla way.
There's nothing wrong or shady either way, but it does make comparison less straight forward.
But that's not all: Tesla adds regulatory credit sales to their "automotive" gross margin figures.
Yes, that's right, Tesla's "automotive" gross margin isn't just vehicle sales like it is for other car manufacturers. For example, look at Q2 2020 filings. The clean-car credits that they sell to other manufacturers are treated as automotive revenue, and that accounting chicanery is entirely what lets Tesla claim a 20+% gross margin on their vehicles. (The clean-car credits are also what lets Tesla claim to be profitable, though it has yet to make a profit actually selling cars.)
Without treating the sale of clean-car credits as automotive revenue, Tesla's gross margins are at best in line with industry gross margins (and fall below industry margins once you apply automotive GAAP to standardize the financials).
The sale of a vehicle results in a credit that can then also be sold, so why can't that profit be tied to the vehicle?
On the flip side, the company can spend lots on R&D that never makes it way into a vehicle. Why should that then count against the profit from selling a vehicle?
I don't understand your R&D point though. It's perfectly logical either way to include or exclude it. There's nothing wrong with how Tesla does it, and there's nothing wrong with how the rest of the auto industry does it. It just means you can't blindly compare the figures.
Either way, adding the $6.8B to their gross margin number for 2019 would have increased automotive gross margins from about 10% to about 15%. Tesla's 2019 automotive gross margin was 21%. MRQ was 24%.
Yeah, I'm not claiming Tesla has bad margins, just that the figures on the balance sheet aren't apples to apples. 10% vs 21% compared to 15% vs 21% makes a huge difference. It's a 40% gap instead of a 110% gap.
As for the evidence, simply read Tesla's SEC filings. The financial parts, not the marketing fluff.