The end of this article says that they plan on starting production early, but then deliveries won’t start until summer. My thinking is that the exceptional “25guns” engineers will be sent to a working production line (Fremont?) for a few months to gain first hand experience on the actual products that he or she will be working on in Berlin. This OJT is the best way to train them so when Berlin gets up and running they will already have experience on the line.
https://www.teslarati.com/tesla-giga-berlin-7000-jobs-january-2021/amp/