I don't mean to advertise for Add-Ons, but thank God for Pet Tracker!
I had an alt in STV doing Archeology digs when I noticed this one Beast marker way off by itself. I moused over and it was a Panther Cub. I looked up the quest and it looked very familiar. But I didn't have the pet in the stable. It kind of bugged me, but I had a lot to do on the alt, so I put it on the back burner.
After doing the tamer dailies much later, I took my main guy to STV. Flew over to the spot on the map. Started looking around and there he was! The cub was sitting there in a cave with a question mark over his head. I did that quest chain close to a year ago and just never saw it. Not only did I kill it's mother, I made it wait for a year on its own (you'd think it would be bigger by now).