No U-Bahn trains from 1975 to 2015?

[Donald C.]

There are only 3 U-Bahn trains available in this pakset, but none of them is available between 1975 and 2015. C series retires in 1975, until IK is introduced in 2015. Why is there such a gap? Is there any addon to add another U-Bahn train back?

[makie]

We count Berlin S-Bahn BR 477, BR 480, BR 481, BR 485 as U-Bahn because they also have a power / electric rail.