My tenants rang me to say the bath had overflowed and the house is water damaged. How can a bath with an overflow outlet overflow?

There are two ways I could think of an overflow.

1. The water was on very high and/or unattended so that the overflow could not work fast enough at the rate the water was coming out, or the overflow was blocked or clogged.

2. The water was almost up to the overflow and a person jumped in really fast, so the water spilled out faster than the overflow could drain.

How can a bath with an overflow outlet overflow? Rose put out the most likely causes. However, There is a third way for this to happen. If there was a bathroom on the second floor and the tub in question was on the first floor the discharge from the second bath could fill the tub up to overflowing if there was a clog downstream from the first floor tub. Do you have more details to give us? Tom