PS: I could use the ID to get unique values, however I can only sort displayed values and I don't want to show a meaningless number (as it would be if I used the ID), so the row number would be ideal.

Try use:

##class(%Library.SQLCatalog).GetCachedQueryTableCount("table_name")

This command will return the number of Cached Queries.

So, you can check if all Cached Queries have been purged.