iCloud backups are incremental. The backup reflects only the current state of the device. So, yes. old backups are overwritten as there is only one device backup in iCloud.
This thread has been closed by the system or the community team.
You may vote for any posts you find helpful, or search the Community for additional answers.
backups to icloud
Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.