"ນາງ" as a general form of address

Hello all!

"ນາງ" is used as a specific form of address:
- "ນາງ+surname" = Mrs...
- "ນາງ+first name" = Miss...

What's the difference in the case of "ນາງ+surname" with "ແດງ+surname"? "ແດງ" originally means "mother", so should we use it whenever we want to defer to a woman?

And to whom can we simply address as "ນາງ"? My dictionary indicates that it can be used for maids. What about waitresses? And saleswomen on the market? And a woman behind a counter? And a random non-elderly woman I want to ask directions to?

Thanks