Forgive me if this is obvious, but I don't get it.
I have four Brooks B17's and they are all different. Two (1950 and 2007) have loops for a bag; the other two (1959 and 1967) don't. Two (1959 and 2007) have chromed rails, the other two are black. One is wide (2007) the others are an inch narrower. The leather condition varies so its quality is hard to judge. Similarly shape and hardness vary considerably but this must be a function of condition so not very useful.
Come to think of it I have seen just as much variation among B15's, but I don't have so many of those; just one, which is indistinguishable from the 1959 B17 except the stamp on the skirt is different, and it's in better condition.
Can anyone explain what is the distinguishing feature of a B17, or a B15 for that matter?