On a number of occasions I have the aircraft type displayed buy there is no data at all in the database.
For example 4A0823 - YR-BAC is showing as a B733 - but if I right click it and locate the mode S code in the database there is nothing there. Even if I look at my local database using the database explorer there is no entry for the Mode S code.
This is strange - where does the B733 come from?