After some investigation these are the instances that are not being used:

• planet4-imagestest
• planet4-en-test
• planet4-buddypress
• planet4-dev-search
• planet4-testdev
• planet4-gulpsync
• planet4-theia
• planet4-testhostpath
• planet4-scssrefact
• planet4-uitests
• planet4-ray-test42
• planet4-thanos
• planet4-test-gcs-usage
• planet4-redhat-* (13)
• planet4-campaigns