"Knocked out" Vs "Fought hard and returned" [duplicate]

So I recently managed to put a few Pokemon into several gyms the other night, and over the past few days, they have returned. However, some have returned with Pokecoins, and some haven't.

So far the only difference I have managed to figure out is the message that accompanies the Pokemon. The ones that return with Pokecoins say

Arcanine has fought hard and returned.

And the ones that don't say

Kingler was knocked out of the Gym.

What is the difference?

So, it turns out there is nothing different between these notifications.

The messages are random - it has nothing to do with who returns with coins, and who doesn't.

You are limited to a total of 50 coins a day. 

Following this advice, I kept watch of my totals, and an eye on the messages that accompanied a Pokemon's return. The messages are purely aesthetic - once you reach a total of 50 coins per day, the rest of the Pokemon will return empty handed.

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