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I agree that it's inconsistent, but we need to have a set of definitions that everyone agrees to. The advantage of the current definitions is that they're completely obvious from the map.

Anyway, I don't want to spend a lot of time arguing about the rules. I'll give you a game under the current definitions and the following alternative rules:
(a) Limited service lines are regarded as being in the same colour(s) as the operator's other lines;
(b) Reversing is allowed at any station.

Do you agree to that?

Clapham Junction to Ealing Broadway without touching the Circle or Bakerloo lines can be done in this way:

Clapham Junction Highbury and Islington West Hampstead Wembley Park Rayners Lane Ealing Common Ealing Broadway.

Of course, the only interchanges between Circle and Bakerloo are Paddington (where the District and FGW block Ealing Broadway), Baker Street (where the Met, H&C and Jubilee make this impossible) and, at the time, Embankment (District blocks again!)