i gotta say, IMO a bonsai is never actually finished, no matter who is doing the care and maintenance, from master to novice. Once a tree achieves the aim the caretaker is looking for little changes for the tree. New growth must be pruned, wired, etc. there's still fertillizing, repotting, root pruning... The list goes on.
The tree will always continue to grow. This growth is controlled, but evenually the tree is in for a restyle, or apex replacement, etc. There are in fact few fleeting moments when you can look at the tree and say, "That's what i was going for!" For that day, hour, or instant the tree is in fact finished...until it changes.
Cord
PS i only have two trees