NG2GB,
As others have mentioned prior, the reason for poor yield is typically from mishandling of the grafts. This may happen in the slivering, storing, placement or whatever. Possibly the tech was on a bender for a couple of days with Thana? Maybe the solution accidentally got some of her contact solution or Jack Daniels in it? Who knows? At a reputable clinic this is likely to almost never ever happen.
The other scenario is that for whatever reason the body rejects the grafts. This is a strange phenomenon and again is likely to not happen. Could it? Possibly. Very, very, rare.