The url is
http://globalstamps.blogspot.comUnfortunately, I wrote about the different editions in a variety of blog posts over the years as I gathered information, so I know it is difficult to get a handle on the differences. Basically, there are two reasons that there are more pages in the four part version of Volume One. First, every country starts on a front of a page. This means that dozens of countries that began on the back of a page or shared part of a page with another country in earlier editions now start on the front of their own pages. More importantly, in the four part version Scott splits out different types within a country so that each type starts on the front of a page--for example, semi-postals or airmails no longer share a page with other stamps of that country. This was to facilitate integration of Volume One with later volumes.
So to make up an example, lets say that all issues of Upper Slobovia originally occupied 3 pages and started on the back of the last page of Lower Slobovia. What you would have now in the Four Part version might look like:
--Blank reverse of page
--Upper Slobovia Regular issues and commems
--Blank reverse of page
--Upper Slobovia Semi-postals
--Reverse of page with remaining semi-postals
--Upper Slobovia Airmails
--Blank reverse of page
--Upper Slobovia Postage Dues
--Blank reverse of page
The bottom line is that there are a lot more blank backs of pages and thus total pages in the four part version than in previous versions.