Hello Mados, and welcome tback to Seven Forums.
By default, Windows automatically saves as many system images as it has space for without taking up more than 30 percent
of space on the backup disk. Once the disk starts running out of room, Windows deletes older system images.
To keep older system images, your clients could use the method in the NOTE box at the top of the tutorial below.
Backup Complete Computer - Create an Image Backup
Hope this helps,