Going to move this to "Telephone Service".
I assume you talking circuit ID. OS type services were a basic voice circuit the last two letters usually defind LS,GS,RD or what every type it was. Since I no longer have the books to look these up can't tell you what NA was and I've never really seen it, OSNC was the most common. Maybe one of our CO guys will know. Also the OS was the Long Haul ID not the local or LEC ID. If your not talking about a circuit ID then I'm not sure what you're talking about.

Retired phone dude