Elson Nova Cat, from the Dragoon Civil War- it goes back that far, it is not a recent trend. BUT as was pointed out the Falcons never went for it from the beginning (IE, no Horse Jade Falcon- just Horse). The Falcon failure to use the Clan as a surname is just spelled out recently, rather than 'not done for unknown reasons.'
For your second part, you are referring to Alexia & Serena respectively . . . and the funny thing is, Alexia Wolf was Jasek Kelswa-Steiner's mattress buddy too.