Is the number of harvestable grafts a lot higher if the patient caught MPB early and immediately started taking action (anti-androgens)?

No, the number of harvestable grafts are fixed for your lifetime and depend upon your original donor density which the doctor can measure. That is why we are careful about what we take from the donor area when we do a hair transplant. As the limit for a typical Caucasian is about 7,500 grafts, then as this number is drawn down, it can’t be replaced and eventually there is no donor hair left. This is my concern in Turkey where they will take out 6000 grafts in a single session, leaving almost nothing left for future balding (which is almost a certainty) and they do it all with FUE, but most people can’t handle more than 3,750 FUE grafts before they start looking bald in the back of their head (see: https://baldingblog.com/collection-victim-photos-internet-harvested-depleted-donor-areas/.