Can agents not written by the same person have the same name? I believe so, as I've found several agents on the Wiki with the same name.
Does it depend, though, on any of the things below?

1. The prominence of the agent
I can see how it would be odd to have two agents named, say, Acacia... but what about a slightly less prominent agent, like Mara? That's a common name anyway.

2. Whether the name was invented by the person who controls the agents
If so, would you then have to ask that person for permission to use the name? What about if they no longer wrote missions or used the agents? What would be done then?

3. The unusualness of the name
If it's an easily recognizable name, like Luxury, I can see how one might not want there to be two agents named that. But if it's a common name in the fandom the agent comes from, would it matter? What about if it's just a common name generally?

4. If it depends on other things, then what does it depend on?

These questions are pretty much hypothetical - I'm just curious, since the FAQ doesn't seem to cover this. Maybe I'm just the first one to ask about it. Or maybe there's some really obvious answer that I'm not seeing...?