I'm pretty sure 4 weeks ago Elon wasn't entirely sure either.
They are very clearly playing it by ear: they are waiting for how well the European and Chinese delivery ramp-up is going, they are waiting for how the China tariff negotiations are going. Then depending on actual numbers they decided, I guess 3-4 weeks ago, to switch gears and do the SR release.
How fast the new SR line is going to ramp up they don't know yet, either. It's a complex, large, football field sized assembly line at the Gigafactory with an unknown S-curve, but that they already made a batch of ~550 units is pretty promising IMHO, it means they already skipped the first 6 months of the Model 3 ramp-up.
But meanwhile they are not over-promising to investors, so Q4 guidance was mostly conservative and the January 30 Cc was a bit upbeat already. And until they didn't know they didn't want to ramp up supply chains, tie up capital, have a higher headcount than necessary, etc.
That's the right approach IMO, Elon promised to not risk the company ever again, so they were ready for a slower ramp-up in 2019. Had there been a Trump Slump and a Trump Recession worst-case in 2019 Tesla would have been ready for it. These were all external factors outside the control of Tesla.
And wherever there is 'change', there is 'fear from change', and where there's seeds of fear there FUD festers.