Hello, my name is Rusty. I do a lot of ordering shirts and glasses, and yes, we provide the PMS code to the printer. Some printers don't use them, they use their eye, in my experience. If you have the PMS code, great. Otherwise, they can match it up with the graphics you send to them.
If you want an exact color, then provide a PMS code and go with a printer that uses them. Otherwise, most printers get the colors close enough that you can't tell the difference.
That part I'm unfamiliar with, I'll open the question back up. Don't rate my service, you may be charged twice.