If he is currently serving time for his prison commitment as well as his county jail commitment then he will not be brought to state prison. It is called a paper commitment. His paperwork will show that he served his 16 month commitment but he will not actually go to prison. If, however, for some reason he was not accruing credits for his prison commitment, then he will be transported to prison to serve the 16 months.
They may have to bring him to state prison to just process him in and back out again.
Seth Weinstein, Esq.
Practicing throughout Southern California
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient factual/legal documentation to give a complete answer to your question and there may be more to the issues you raised then I have set out in my brief reply.
It depends on what credit he has on each case. They are calculated separately, and it depends on exactly what sentence he got at each stage. Call his lawyer and ask.