Can you quote the text here? For the life of me I can’t find the section you’re referencing. I’ve heard the “timing production to match tax credit” thing before and it doesn’t make sense to me, hence why I’m trying to track down the primary source.
Phase out starts with the same tax credit still applying for the remainder of the current quarter and the next one (before being reduced in later ones) and that's exactly the reason why they would want to match reaching the threshold to the beginning of a new quarter. This way they have as much time as possible to ship as many cars as possible to their customers (that's OK then since numbers sold do not affect the phase out beside the threshold of 200 000 cars).
Tesla is near the 200k mark and has been holding back domestic sales so to hit it at the beginning of a quarter (i.e now).
Edit: Here is a link to the official explanation of the credit in glorious IRS legalese (https://www.irs.gov/irb/2009-48_IRB#NOT-2009-89).
Relevant quote from the IRS to this discussion:
"The new qualified plug-in electric drive motor vehicle credit phases out for a manufacturer’s vehicles over the one-year period beginning with the second calendar quarter after the calendar quarter in which at least 200,000 qualifying vehicles manufactured by that manufacturer have been sold for use in the United States (determined on a cumulative basis for sales after December 31, 2009) (“phase-out period”). Qualifying vehicles manufactured by that manufacturer are eligible for 50 percent of the credit if acquired in the first two quarters of the phase-out period and 25 percent of the credit if acquired in the third or fourth quarter of the phase-out period."
This is what is confusing me: if the credits are timed to domestic sales (so international sales don’t affect the timing of the tax credit phase out) what does this have to do with production?
Rather, you don’t want to rush to produce vehicles you don’t want to deliver quite yet. You want to get to maximum output at the same time the timer starts on federal tax credits phasing out (which, keep in mind, would’ve happened without Model 3 production due to 2k/week Model S and X production).
tl;dr they'd basically benefit from an additional 336M in government subsidies if they delay recording their 200k'th sale to July 1 instead of June 30.