How positions are worked out
STIB doesn't publish GPS. Every 20 seconds its feed says, for each vehicle, which stop it last passed, how many metres ago, and where it's heading. This page puts the vehicle that many metres along the line's real route (from STIB's timetable shapes), then glides it to the next reading, so a vehicle is drawn about 20 seconds behind reality. Zoom in: trams, metros and buses are drawn at roughly their real length.
"Usually … late" comes from Brussels Lakehouse, which has been recording STIB every 5 minutes.