How to address outer/inner envelopes for formal invites

AmJam04

So, my question is the title, basically.

We're having a formal (black tie) wedding and need to address the invites as such.
Could I have an example of what to put on the outer and inner envelopes (names-wise. I know about how to write-out the address)? Everything I have read kind of conflicts with each other and now I'm just confused...

AddieCake

I usually use Crane's to answer addressing questions. It has links that tell you what to do "If this, if that."  

http://blog.crane.com/2012/02/03/wedding-etiquette-how-to-address-your-envelopes/

AmJam04

Ooo, I like that site.

So what about guests? We're putting the SO's name on the envelope (no "and guest") but would their name only go on the outer envelope if the two live together? If not living together, then the SO would just go on the inner envelope, right?