AFAIK you need an OW cert to take a nitrox course. I have a dive buddy who carries only his nitrox card. This is because he was certified decades ago and the card is decintegrating. He still has it, laminated. However it's not something he can carry. A replacement isn't possible because SSI bought the company and stopped issuing replacement cards after claiming records were lost in a fire.A Nitrox card does not require any dives. I would not expect anyone to take my Nitrox card as proof that I am certified to dive. Much less proof that I am good for an "advanced" dive. Heck, I got my Nitrox card as soon as I finished OW, before I had any post-OW dives at all.
My point is, he uses his NAUI nitrox card exclusively. It's never been a problem that's worth the huge cost of an additional scuba class to remedy. He did take a refresher with NAUI 4 or 5 years ago, but no card was issued for that.