What Bob said is true as well and I can vouch for that personally. Before 9/11 baggage was still not supposed to get on the plane without passenger. On trip to Cancun via Newark my friend's and my luggage got on the plane alone.
Due to an agent on the first leg letting my friend get on an international trip when her birth cert. had her maiden name and her driver's license her married name and saying it was okay when we got to Newark the agent would not let her board our flight. So we went to baggage to get our luggage and nobody knew where it was. Well, it was on its way to Cun. We spent the night in Newark with some toothpaste and had to purchase other clothes. Her papers were fixed and we had to take a flight next day via Houston. That flight was delayed and we were put on a flight to Mexico City and stayed overnight there. A baggage attendant in Houston told us our bags were in Cancun. I have traveled the world. In Amsterdam on way to Africa, I lost a piece of luggage that I was told in Boston I could pick up in Holland. The baggage people in Amesterdam were so nice and finally found that luggage was in Africa crate. The attitude of the American agents was so different except for the one in Houston. Anyway, got to Cancun about same time as it took to get to Tanzania and there was our luggage on vacation all by itself!