Rob,
I think it depends on how you search the database - I've just looked for A320's at EHAM and on the map it shows two and also on the Lock Flights browse dynamic flights timetable it shows two IF you narrow down the options to only look for A320's.
But if you don't narrow the search and leave all options as they are by default it just gives you the first 30 planes, which on my search did not include either one of the A320's so it would then appear that there weren't any (as there's no button to go to page two of the search results).
Does that tie in with your experience?