As you say you only save the distinct values to the database, generally RadGridView will not replace its items until a new query to the server is executed and all the data is fetched again.
Basically you could hide particular rows by adding a FilterDescriptor that filters your items by a certain criteria (in your case you need to have such a boolean property). You can then define the Filtering criteria as explained in the Programmatic Filtering article. As another example, you can check the "Programmatic Filtering" WPF Demo.
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