Looking at my own model I come to similar conclusions. According to my information, which might not be the newest and most accurate any more, but should not be too far off the current planning at Boeing, the complete production rollover from the current B777 Classic to the B777X should be done by early 2023, as is shown in Scotts picture.
According to my math and including the six aircraft which were booked in January I get a gap of 249 aircraft which needs to be sold to keep the production rate at 7.33 until the B777X takes over full production in 2023. I started the 7.33 rate in Q2 2019 here, when the B777X "feathers in" the production (using "Boeing tech talk" here).
If we go down to a rate of 7 aircraft a month in early 2018 we would end up with 214 open production positions.
I think this clearly shows the need of a rate cut for the B777 Classic and that this rate cut has to come soon. We will see how hard analysts will question Boeing today on that. But meanwhile it seems that Boeing acknowledged that need...
UPDATE: Boeing just announced to cut production to 7 aircraft per month in 2017. When I put that into my model, Boeing is still 198 oders short. This first production cut of the B777 Classic might not have been the last one.