Red Flag 2-class unit number 5385, with the later-style square cab, was built in 1980. Parallel to the introduction of the Red Flag 2 came the Man'gyŏngdae (만경대호) class. These had late-style Red Flag 1 body work, but were geared for higher speeds for dedicated express passenger service; they were painted in a cream over red livery and numbered in the 5200 series. These produce and were introduced in 1980. Over the years, many Red Flag 1 and Red Flag 2 locomotives were modernised. Upgraded and rebuilt units are given a new class name, and can be identified by the addition of the new class name in large lettering - either painted on or using characters cut out of metal. These include:  Running numbers are allotted in the 5000, 5100, 5200 and 5300 series, but the assignment seems haphazard, with many units of Red Flag 2 design carrying lower serial numbers than some Red Flag 1 units. The 5000 series consists entirely of early-style Red Flag 1, and the 5100 series is almost entirely early-style Red Flag 1, with one anomalous unit of Red Flag 2 design (5103); this may be a case of a scrapped unit's number being reassigned. The 5200 and 5300 series are a mix of late-style Red Flag 1, Red Flag 2 and Man'gyŏngdae-class units. While it is possible that 387 locomotives were built, with simultaneous production of both designs, it seems more likely that as the Red Flag 2 were being built, existing units of the Red Flag 1 type were rebuilt internally to Red Flag 2 standard and given new running numbers. This would fit better with the information that around 150 units were built in total. However, to add to the confusion, over the years many units were upgraded and rebuilt, and given new class names, whilst retaining their original running number.