*nods* It only works for kitties born in world. Like Kayla, most of mine are born in world, but not all of them. It does miss the ones born in the online cattery...but for me, that's usually just the OS from my Fancie. She stays online for safe keeping & careful monitoring.
(I'm the opposite of Kayla, in that I keep milk in my Online Cattery, but cuddle the In World ones instead. I usually only have my <7 days ones, seasonal/extra permas and Fancie in my Online Cattery, and then send the Fancie's current partner there when she is within a day of being ready so I can sync up their energy levels.)
Also, if you have two born at the same time, it only reports the last one. That bug has been reported, but I hear it's not fixed. I think it had to do with how the info comes from the KC's server.
If you have KittyCats breeding on more than one SIM, you can put out a sensor at each location and they should both update your signature - at least that was how it worked when I first started testing it. I have had them all in one place for a while now.
And, yes, you have to copy and save the code into your signature here, but only once. Then it is automatically updated.