It has since been converted back to a regular carriage, but it continued carrying number 4444 at first. After its revision in 2011, this unit was given its original number (4231) back. The train's name Koploper means "Frontrunner" but the name can also be seen as a reference to "walking through the head" ("Headwalker"(Dutch: "Doorloopkop")). When ICM units joined, the doors at the end of the train would come out, and a walkway would emerge, coupling with the other set and allowing passengers and crew to walk through to the next set. (This makes it easy for conductors to check tickets and check on the security of the passengers. In addition, each set had catering cars before they were abolished in 2003.) However, since 31 October 2005, these were put out of use. The reason given was that they were not often used, but they also had many technical problems that made the trains late on a regular basis. During their refurbishment from 2006 onwards, these hallways were permanently sealed shut and the doors at the heads of the train were replaced by a light polyester plate, saving the NS maintenance costs. From November 2006, the Koploper went through a process of refurbishment. The 4011–4097 series first went into a renovation. The first train left NedTrain's workshop in Haarlem in April 2007 and then put into the regular service. To distinguish the not yet modernized sets from the modernized sets, modernized train sets are referred to as ICMm. These sets feature new interiors with 13% more seats. One could distinguish apparent differences between 1st and 2nd Class. The first class consists of red seats and second class consists of blue seats, equal to SGMm units. Meanwhile, one improved the wheelchair toilet, installed air conditioning, OBIS, and digital travel information. On the exterior, the train sets were repainted showing blue window surrounds curving at the ends of units. Numbers are now nearer the front of the train. The connectors diverting the train compartments were revealed and digital destination screens were put at the trains ends. The renewal of the series 4011–4097 completed in June 2010. Refurbishing and renewing of the 4-car units took place between February 2010 and July 2011. Between 1986 and 2002 many sets featured adverts.