Mary calling Lou "Mr. Grant"

I'm not sure. Some companies are more formal than others.

In Mary Richard's case, when she interviewed for the job she was being polite and adhering to protocol. Afterwards it seemed awkward for her to call Mr. Grant 'Lou'. Maybe it was an age thing. Ted and Murray were closer in age to Lou Grant.

Later on I suspected a different reason. When I found out that Mary Tyler Moore's husband was GRANT Tinker, I figured it was a way for her to say her husband's name in every episode. Just like MTM had her son's picture in a frame in Mary Richard's apartment, just a way to involve the family. Who knows?

I can't remember the episode but she tried calling him Lou and it didn't feel comfortable to her.

One of the idiosyncrasies that defined Mary was her deference to others. I believe in a later episode Lou tells Mary that he hired her, in part, because she apologized to a desk that she bumped into at her interview. Someone who is deferential to a desk is going to be hard pressed to get on a first name basis with their boss.

It's also a form of respect. I've been seeing the same doctor for 25 years, but I can't bring myself to call him "John."

Jesse calls Walter “Mr. White”. Even in the crysral meth world there’s old-fashioned respect for one’s elders.

In 1974 I still called my boss "Mr. Moore". His first name was Harry, but I never addressed him that informally.

Didn't Lou and Mary almost share a romantic kiss one episode? Seems like they went out for some reason, know they were very fond of each other and couldn't think of why they shouldn't share a romantic moment. But they couldn't stop laughing at how awkward it was. If anyone wants to confirm this, I'll be happy to hear it. What a funny and charming moment.

I do think Mary got into the habit of calling him Mr Grant and was simply used to it. He did cut a figure of authority. I like the Grant Tinker theory.

In 1974 we called our boss Mr. Moore. Not uncommon at all.