Tesla says GF3 battery module production will be online this year, concurrent with stamping, joining, paint and final assembly. In theory they could send GF1 cells to Shanghai, but there's no reason to send packs. Unless they've changed plans again, of course.
Instead of theorizing a huge stash of packs somewhere, common sense says the 6k/week reports were simply wrong.
I agree that it seems unlikely Tesla would stockpile packs. However, based on news and comments from Elon and JB over the last few quarters regarding grid solutions and ramp in TE, it seems possible that the reported 6K/week pack production and potentially excess capacity from low TM production are going into TE products. Some of the new battery/pack lines that were installed in Q4 are likely for TE. We could be in for much higher revenue from TE than people are expecting. The low margins will be resolved with higher production and economies of scale ultimately reaching at least 25%.