I know you are supposed to avoid this.
But what does it actually do to the belt if you do get some on it & it doesn’t get cleaned off?

I don’t know if I got any on a belt or not. It is a possibility & since I changed the coolant recently one of the belts squeals .... but only for a short time after starting a cold motor, & not at idle, just under a little load. It stops after a minute or two.

If this has been caused by coolant getting onto the belt ..... will it get worse or better over time?

Car has only been used 2 or 3 times since I changed the coolant.