You'd have to know the size of the order book for Model Y in N. America. It's very possible that Giga Berlin is producing Model Ys before N. America has satisfied the backorder demand.
The 2nd issue is spare Model 3 capacity. With Europe having only the ability to purchase Model 3s for the next 1 year+ its a highly effective backstop to maintain demand for Fremont Model 3s if N.American demand shifts strongly toward Model Y during the period of backorder production.
Cheers!
Yes, those are both possibilities. Other possibilities include (1) Model Y ramp is slower than expected (unlikely IMO); (2) Tesla is battery constrained so doesn't mind starting Model Y SR+ early to free up batteries for GF Shanghai Model 3, Semi, Megapack, etc. or (3) GF Berlin Model Y production starts ahead of schedule.
Even with all those possibilities, I still think the most likely scenario is Tesla ships some Model Ys to Europe in advance of GF Berlin production.
Either way, one thing this discussion drives home is how far Model Y demand outstrip supply this year as Tesla ramps up production at Fremont -- a great problem to have in the midst of all the coronavirus inspired turmoil.