The figure for missing/incorrect Heathrow flights typically runs at around 10-15%.
Yesterday's total wasn't quite as bad as normal, but still includes lots of flights that operate every day (for example BAW38TP LROP-EGLL).
And bearing in mind that there are literally dozens of sharers in and around Heathrow feeding arriving and departing flights into the network, it's crazy that the server persists in telling us that, for example, CPA007 is a Hong-Kong-Delhi service, or that Shuttle 9J (inbound every afternoon from Edinburgh, for donkey's years) is a mystery flight with unknown origin and destination.