The German site only shows true availability for BA flights, when control of the flight is transfered to the airport (dispatch) - roughly 24 hours before departure.
Then it goes from understating the availability to over-stating it, as it shows the number of unsold seats, but does not recognise things which the airport have done such as upgrades; blocking off seats for any reason; allocating crew seats etc.
Understanding this is where the upgrade art comes in!
On a recent flight, I boarded, sat in a full F cabin, logged onto Gallileo and it still showed 5 seats available.