DistrictDriver wrote:

Basically, any of the services via Edgware Road would have to be C
stock, as the D stocks are too long to fit in the platforms (and I
believe they scrape the platforms!). I think there's also a
restriction on C stocks going any further east than Barking, although
I'm not sure of the reasons.

UIVMM it's because C stock can't go as fast as D stock, so would cause
delays.