what is the chance that hair will not grow from an ht? what about if someone wore a hair system before? what about if a person had a couple bad hts before finding a qualified, world-renown dr?

The success rate of a HT is almost 100%
If a qualified skilled surgeon performs it.

I have worn a hair system through 4 Ht and all the hair grew in perfectly.

My first Ht I didn't use glue for about 1 month after the HT and than glued again and they grew fine.

Second same thing.

Because of the first 2 I was able to cut the hairsystem in half and went for the remaining 2 by clipping the mini size system on after the HT.

NO WORRIES, JUST BE CAREFUL RIGHT AFTER SURGERY!

The only downside to a bad HT is the depletion of the donor hair. A skilled surgeon can do a great repair job!

I have to say the respone from Hairseeker is right on the money. I have only heard of a few documented cases of the x factor which is when for some unknown reason a patient gets no growth.
In the hands of a skilled hair restoration surgeon your success is almost guarenteed. I have performed hundreds of cases on patients who wore hair systems and there have not been any noticable differences in the results from those who do not. I do recommend no glue for at least 1 month following the procedure.