Ring of the Cat Lord eligibility...

[Conundrum]

Was just wondering - I've seen a few instances where I've killed a cat for the first time and it hasn't generated the "spirit rises from it's corpse, wails mournfully then plunges into the ground" message. It just happened again, because I stumbled into the damn cat while I was confused. I checked :k and it's the only cat listed, so it's not because I've killed a cat previously. Does this mean that the kill didn't count to anger the Cat Lord? Or is that message only generated sometimes? (dependent on Pe or something?)

[Laukku]

The message does not matter - if there are any felines in your kill list, the Cat Lord will hate you.

[Soirana]

The message does not matter - if there are any felines in your kill list, the Cat Lord will hate you.

To be exact felines in kill list upon enetering cat lord level.
You can do with cats whatever you want in period between generating cat lord and speaking with him.

[RndmNumGenerator]

The message does not matter - if there are any felines in your kill list, the Cat Lord will hate you.

Not exactly. If you have only killed only one (rarely this will happen with two) the Cat Lord may not be hostile, however, he will not give you his ring either. There is a good chance he will become hostile later on, like many other non hostile monsters do.

A good way to check and make sure before finding him is as soon as you enter his level, scan the monster memory for all three cats. If you killed one and didn't know it(hit with bolt/ball out of visibility range) it will still be recorded in there.