Couple of items:
Most reports are that when a patient goes on a ventilator vast majority never come off.
Prediction models indicating a ventilator shortage only account for total uses. Does not account for the fact that being on a ventilator is not a long term solution. It either works or does not work in a short time frame. Then that asset goes back into the inventory. From what I can see the models only recognize a single use of the ventilator.
But the bigger factor is ventilators are not answer medically. This story is emerging quickly.
Maybe you're failing grass the point that the numbers of people needing the ventilators vastly exceeds the amount of ventilators on hand if you have 10 ventilators in your hospital and 20 patients needing them what's your course of action? This is why they're calling it a shortage not because someone goes on and it can come off and use it again it's because of the amount of people needing it at the same time