It's not just joining to two halves together:
...we will transition a single piece casting that also integrates the two rear crash rails,” Musk said
The Redesign Of The Tesla Model Y Body Was Inspired By A Toy Car
Would you know the highest VIN to date?
I refused a Model Y in August (bad fit and finish) and am holding off until the Model Y production transitions to the single-piece casting that also integrates the rear crash rails.