A lot starts with a yarn order, roughly five months out. The mill knits a sample length, we wash it twice, wear it for a month, and then decide whether to commit. Most do not make it past the wash.
Once a fabric is approved we grade the pattern across the full size run and sew a first piece in every size, on a body, not a mannequin. The measurements published in our size guide come from those garments, measured flat.
The workshop then cuts the whole run in one pass. When it is gone, it is gone — we would need a new yarn order to make more, and by then we are usually working on the next thing.