That's where you're wrong. 3501-4 are connecter to driving trailers 4096-9 as two-car sets. Hence, the first motor car connected to a T trailer is 3505, connecter to T4171. 4171 - 3505 = 666, not 670 > The first C code car is 3501 > The first T code car is 4171 > > 4171 - 3501 = 670, not 666 > > It's only 4246 - 3580 = 666, not others.