On https://commons.wikimedia.org/wiki/Commons:Monuments_database/Statistics we have a report of all the sources we index. Only sources for which we find records show up here. Things like T203348 are very hard to detect right now. Shouldn't be too hard to also go over https://github.com/wikimedia/labs-tools-heritage/tree/master/erfgoedbot/monuments_config and add these as empty sources and maybe overwrite it with the real data based on the database query. That way we always include all configured sources in the report.
Current code is at https://github.com/wikimedia/labs-tools-heritage/blob/master/erfgoedbot/database_statistics.py