I ought to have paid more attention before, but how the eck can
Fenchurch Street to Bank be an OSI when Cannon Street to Bank is not?

Perhaps even more to the point, why are Liverpool St NR to Bank LU, Waterloo
NR to Embankment LU, and Waterloo East NR to Embankment LU all considered as
OSIs when Cannon Street to Bank isn't? It doesn't seem to be an even playing
field.