That's what this protocol avoids doing. By using your own adult stem cells that are already widely distributed in all the right places, you can duplicate them any number of times without the problems of injection that put too many in one place and not enough in others. The drawback is that adult stem cells are not pluripotent, thus must have some partial methylation (or histone modification) that prevents pluripotency. If these methylated genes also age epigenetically, daughter cells will have a mixed age, with some genes young and some old. But that's exactly what happens normally when stem cells differentiate to replace aged-out somatic cells, except here we are artificially accelerating the process.
I suspect, however, that there are pluropent cells still lurking in the body, and these have not been discovered due to their very small numbers. If supplying their specific nutritional needs--the amino acid threonine--promotes them at a greater rate than adult stem cells, then daughter cells from those pluripotent SCs will be fully age reversed and the average age of all genes will be brought down (though some a lot more than others).
Yes in vivo treatment is certainly preferable; let's hope we can sort out a reliable source of stearic acid and see if a decent number of people can get results from this. I still have an epigenetic blood test in reserve. Once I have re-started this protocol and done 20-30 iterations I'll test again.