Pam, now that you mention it, I'm not sure if those things that were outside were left behind or just copied. I do remember losing my cop car in a previous game after a move once. It wasn't in any sim inventory or my family inventory. I've also read posts from other people who lost the cop car after a move. I used the mailbox cheat to become a lieutenant again and get a new one.
As for everything else I saw on the lot outside, I did not check to see if it was in my family inventory. I assumed seeing it there meant it wasn't, but the sprinklers were copied, so maybe everything was cloned, too. Regarding the music box, it's just gone. No big deal, I bought another one.
Inventory is a funny thing sometimes. My sim stole books from the French bookshelf he was reading when the trip ended. (and no, he's not a klepto) It was a race against the clock to see if he would finish the last book for the read 50 books wish. The message popped up and said it was time to leave, but before the loading screen came back up for sunset valley, i saw the points thing flash. When he got home, that book was in his inventory. After reloading the game, another French book spontaneously appeared in his inventory. I sold them both.
In addition, I know on my first trip to France that I bought grapes from the special merchant. They disappeared when I came back home.