I concede, and give way to you, good sir. You have eloquently described line forms on a digital map of railways in a simply exquisite way. (In all seriousness, I now get that a casual mapper like me shouldn't really mess around so eagerly in future.)

Smoothed out curve:
changeset/63428075#map=19/51.53941/-0.12733

Reshaped crossover and running lines
changeset/63428360#map=18/51.54075/-0.12336

The NLL link curve is connected to the line between the CTRL Up and Down when emerging from London Tunnel No. 1.

You're right about the passive provision, sorry about that, but in the previous versions, the running line and the trackbed were confused at the bridge over York Way.

Ironic about that sharp curve, missed that one when smoothing out the others.

The Silo curve/NLL link junction is shown to be just before the bridge over the MML

The CTRL relief/down junction is directly underneath the CTRL-NLL link line as edited

What have I messed up?

Is the damage to the actual tracks? Because I was fixing errors in the way the track was laid; there were some tracks that magically turned into footpaths, some very sharp turns and corners, e.t.c.

Yes, I remember now, I haven't made any similar mistakes, thankfully.