That is probably a good question for chainstay length expert
RiddleOfSteel . The numbers I gave the other day were measured as you described - center of BB spindle to center of dropout slot.
On the Raleigh/Carlton brake length topic I can offer this data:
1969 Professional Mk 1 tubulars 610 front, 750 rear
1973 Super Course 27 x 1 1/4 750 front, 750 rear
1974 Super Course Mke II 27 x 1 1/4 610 front, 750 rear
1974 International 27 x 1 1/8 610 front, 610 rear
By accident or by design? Certainly not consistent.