The platforms at Holborn Viaduct only ever did take 8 cars and then only 3 of the original 6 platforms at that. These were the only ones which were electrified and were extended on the early Southern Railway electrification. The remaining 3 were non-electrified and rather shorter (there being insufficient throat width to lengthen) being used primarily for parcels traffic. Later these latter 3 platforms were demolished and the track removed.