I always thought a livery was just whatever you kid decided was their comfort item, whether it was a regular stuffed animal, a washcloth, a shoe, whatever.
Both my kids have 2 things they’ve slept with since they were babies-1 regular stuffed animal and one blanket animal. They’re now 4 and 7. The 7yo sleeps with a bed full of stuffed animals now, but she has to have her main two every night still.