I don't know for sure if that is true or not. I would say even if they do now the fact that they have traditionally done so little testing on ICE cars will mean that as EVs become more common that percentage will drop in line with ICE testing.
From prior reading I get the impression that they get signatory approval before you can slap the "EPA MPG" or "EPA Range" on the sticker but it's up to them if they test your vehicle or not.
And 100% of what. There are dozens of configs of Tesla Model S and in reality they should have dozens of EPA ranges but if you go look less than half the Tesla configs have the unique EPA range they should. In some cases Tesla has had a modification out and in production with a provisional Monroney sticker and an asterisks on the web site with that number provided from the prior version and updated later. Literally customers get sent a revised Monroney sticker.
I think under the strictest math you would say they approved ratings for half the Model S configs between 2012 and now. I'd expect similar grouping to apply to Model 3. They'll get one or two configs tested and everything that goes out for a year or two will share the same "epa ranges" but in reality there will be various ranges depending on your actual config.
No matter what the websites say I wouldn't bet my life on it that a physical car made it for testing before the first delivery with no significant differences vs the cars delivered. The phrase "its close enough for government work" applies.