Does someone know about the development of American robin songs?

I've been listening to the robins that live in the neighborhood, and followed their development over years. We've got one that's beat the odds, and has been returning for almost 10 years now. He's had multiple broods, who have themselves gone on to populate the neighborhood.

Over time, I think I've found these details about robin songs:

• Each robin sings his own song, for mate attraction and for territory marking
• The song will have some elements that are regularly returned to, but they are constantly trying to add new melodies
• The best melodies start being copied by other robins, but probably not as well
• A young robin (yearling) still needs to practice singing, but he will learn quickly
• Younger robins have simpler songs with fewer different parts, while older robins will have larger repertoires
• Still, a young robin with just the right single melody can start getting other robins trying to copy them

Am I right about this? Is this what the science shows?