As previously stated, Xray will only index and scan newly added artifacts to an indexed repository. To index pre-existing artifacts you may use the option of ‘Index Now’ in the UI.
Navigate to the admin tab → Xray → Settings → Indexed Resources. Select the "Index Now" option on the right-hand side, as depicted below:
Once "Index Now" is selected, additional options will be presented for selecting which artifacts in the repository should be indexed, as illustrated below:
After selecting the desired artifacts to index, they will be indexed and appear on the Scans List for scanning shortly thereafter.
You can watch a demo of these steps and access additional troubleshooting information concerning the indexing of pre-existing artifacts.