Diamond T model numbers

[Rolf S. Ask]

David

I follow you on your thoughts..

I agree the "9" would be the class of the vehicle (including the 980/981)
I am also pretty sure the prefiks A and B represent the Year, i.e. those without any prefix is 1940/41 models, those with A is 1942 models and B is for 1943 and onward models.
But then the second diggit....
It can not be for the wheelbase, nor the number of axles. Not even the wight limited on the payload allowed.
I'll try to explain my toughts;
Wheelbase: the 967, 968(A)(B), 969(A)(B) and 972 have all the same wheel base. And 970(A) and 972 have also different wheelbase.
Number of axles: Why then different second diggit?
Payload: Also why different diggits.
Bodytypes: Well can't be that either. 968 and 969 is the cargo and the wrecker so they have for sure differrent bodies....

So as more I am thinking on this, the more I.. or less I understand.

Any good ideas?
I am sure someone out there knows this and could sheed some lights on it. And also guess it is obvious when explaind to me :-)