This is just me spitballing against the wall, I have ZERO INSIDE KNOWLEDGE whatsoever. I dont work for Tesla or anything, I am just a volunteer here at TMC.
With that out of the way, my guess as to what has been holding this up is that it has something to do with Tesla getting reimbursed for the Tax credit. It feels to me like they need "something" signed off by the govnernment before they can claim the credit.
Documents cant be back dated (legally at least) so, hypothetically, if they needed some approval on something / something signed off by some regulatory body, but delivered cars before that, any car delivered before "whatever it is" was signed, Tesla could not get reimbursed for any tax credit they likely already gave to the buyer.
Just thinking out loud here, but its what it feels like to me.