Do you know if this was a concrete pool or a vinyl pool?

Depending on the fill material used and the compaction rate during the fill in process, it will determine how much settling to expect.

If this was performed a coupe of years ago and it looks ok, chances are the settling has occurred and perhaps the yard was maintained during that time.

Some towns require complete removal of a concrete pool. Some allow for partial demo and burial. In this case the floor of the pool must be opened in a few spots to allow potential ground water to pass through.

Vinyl pools must have the walls, liner removed.

Clean type fill, free of tree roots, leaves, must be used in this process to prevent as much settling as possible. Some towns may want to inspect the fill material prior to use.

Settling will to be expected on a project like this.