I was able to get ahold of some of the text (no illustrations) from RRC volume 1. In the appendix, he admits that the arrangement of the quadriga coinage is particularly difficult, with the various styles shading almost imperceptibly into each other.
The sequence of quadrigati begins with no. 28, with the obverse in high relief, circular ringlets of hair on top and long, neat, curving sideburns. The reverse has both Jupiter and Victory both standing in the chariot, incuse legend, but also includes a mixture of incuse letter-forms and letter-forms in relief.
So, my coin is Cr. 28? Not so fast!
The most distinctive feature of the second sequence (no. 29) is a legend placed on a tablet shaped like an inverted trapeze. So then Cr. 29? It would seem so, except the inverted trapezoid is also described in the third sequence!
The distinctive feature of the third sequence (no. 30) is the stance of Victory not in the chariot, but on the tailboard, so that the whole of her figure is visible. This group has an obverse with either harsh or rather stupid features and legend in rectangular tablet or an inverted trapezoid.
Carthage's example is anything but harsh or stupid!
I'm not obsessed with attribution, I just prefer to have it accurate. 
This is a toughie.
Crawford's main arrangement has some merits but an equal number of problems. There are basically five relatively common
types- early
RRC 28 with
incuse legend on a raised rectangle. Pl.II all, Pl.III all. There is of course a lot of development from the earliest finest
style pieces which the Sheikh paid CHF 190,000 for an example once, and presumably later coins,
still of
good style but not so beautiful. But there's no clear dividing line.
- late
RRC 28 with
legend relief in a frame and a dumpy
flan. Pl.IV, 1-5,8. I don't think these are necessarily from the same
mint given the massive difference with the early
types but at least they are easy to distinguish. These go on to become debased
-
RRC 29 with the
legend in relief on a raised trapezoid. Pl.V, 3-4
-
RRC 30 with
Victory outside the
chariot and a narrow
head. Pl.VI, all
-
RRC 31 with V truncation with dot under.
Legend may be
incuse, mixed or relief. Pl. IV,10.
95% of quadrigati fall clearly into one of these five large groups. Despite the
RRC 31 which I cite being illustrated by only one plate example it is actually abundant. Likewise the later
RRC 28.
None of these five major groups should in my view be eligible for
head to heads BOT between the groups. They are distinct and common enough that there should be
head to heads only within the group.
Of the remaining 5% including the supposed
RRC 32, 33 and 34 which by taxonomy are all just minor variants of the early
RRC 28, I just cite the closest
RRC plate match by
style, and then assign to one of my five main boxes above (regardless what number
Crawford placed it in). So, in my usage, Pl.V,1-2 don't have the relief
legend on a raised trapezoid characteristic of
RRC 29 (Pl.V 3-4) and I tend to lump them with the early
RRC 28 group. And despite
Victory not being outside the
chariot, Pl.V 7-10 exactly match the
style of all the Pl.VI
RRC 30 coins so I regard them as
RRC 30
So that's my system. Five main
types, and any variants that don't automatically fall into those
types, I cite the closest
RRC plate match and then assign to one of my main groups by a pragmatic allocation that in some cases overrides Crawford's thinking. It's the best that I can do.
As for Neomantor's desire for accuracy, that would be an ideal if the taxonomy was clear in the first place. It isn't, it's a
bit muddled. So we have to be pragmatic and look at the apparent major groups. You do need the
Crawford plates for this. The text alone is no use. Neither are any online resources useful. Without the plates all you can say is "this is a
quadrigatus".
In my view BOT competition should not pitch any of these main
types against each other. It would be akin to allowing an archaic
owl to compete against a classical
owl. The more classic look would always win, and in this case we would always end up with just a single early
RRC 28 in classic
style in the BOT. At least we need the main variants represented by their own coin in the BOT. In my own
collection I have very beautiful examples of four of these
types (and a worn example of the fifth). I never see them as competing. They are different coin
types each beautiful in their own way.
