Well, OK. But the rolling stock on those lines is (in some cases) shared between the lines. The same train could end up operating the Circle, District, or Hamme

Well, OK. But the rolling stock on those lines is (in some cases) shared between the lines. The same train could end up operating the Circle, District, or Hammersmith & City lines. Parts of the track are also shared between those same lines, so I guess TfL wanted some consistency.