Per ASCO presentation 12K a year is max capacity of current clean room GMP process not Flaskworks. So many more than 12K patients a year with Flaskworks will be treated at a small 90K square foot facility.
In my opinion, given the size of the machines, Sawston should be able to treat north of 250K patients a year assuming staffing levels can be met to operate Flaskworks at that scale.
I don't think that will be an issue given the global surplus of postdocs working at Starbucks.