Have I lost of grafts 4 weeks post op after scratching off crust?

After 4 weeks, your grafts are secured. It is normal to experience shedding. If you are concerned, please follow up with your surgeon for an exam.

It is unlikely. After 4 weeks your recipient should look nice and clean without any scabbing. We know that transplanted hair is completely taken after day 5 and even if you try to pull hair shaft, the follicle stays and grows new hair. 

At 4 weeks you will not have lost grafts other than the crusts that you have left on your head. I performed a study on graft survival and after 2 weeks, you can't damage the stem cell below the skin which were attached to the graft