This much is true. I had observers turn up to.games I'd taken last minute so hadnt sent to the county for observation. Again, I bet this differs per county.My county provide a spreadsheet that we, the match officials, have to keep up to date and submit at the end of the promotion period.
However, my County also tell us not to cherry pick games that we submit for observation, as they do know the games we are appointed to.
Whether they know this through regular updates from affiliated leagues through out the season, or at the end of the season when they collect club marks etc I don't know.