It is mostly related to how the exam portion is calculated. The 1995 guidelines are similar to how the EM guidelines in CPT tells you to calculate the exam. See definitions for the following
Problem Focused
Expanded Problem Focused
Detailed
Comprehensive
When you read the definitions especially between Expanded Problem Focused and Detailed it was a bit vague as to when you would bump up to a detailed. So the 1997 guidelines were born with very specific items to be counted up to let the coder/auditor know exactly which level of exam they had.
Here is a related article on EM University site which I greatly respect
http://emuniversity.com/FAQ/EMFAQ3.html