Is it a '31 or a '32

EDIT:  Posted by Carl in the old forum.  - A.J.

In the course of compiling a registry for Royales I got to wondering.  On the members only page of our web site there is a list of all REO serial numbers, by the looks of it compiled by Ray Wood long ago.  For the 8-35 model it states the serial numbers in 1931 went from 35N1 up to 35N2711, so 2711 units of Royals on the 135" wheel base manufactured in that year.

For 1932 it says the numbers went from 35N2712 up to 35N2875, or only a measly 163 units manufactured that year.  What is/are the difference(es) between a '31 and a '32?  Anything in the body or equipment where one can look and say, this is a '31, that one is a '32?  Or is it simply that 35N2711 was manufactured in December of 1931 and 35N2712 was manufactured in January of 1932?

Just wondering,

Carl