Back in 2006 stamp grading and valuations started to gain immensely in popularity. There were many different charts and tables showing different aspects of grading, stamp condition and valuation calculations.
I started to research these various venues and compiled a chart that put much of it into one table. It is not a "definitive" piece, but it does help one understand the factors that affect how a stamp's value when considering its overall condition compares to the stated catalog value.
If you'd like to get a copy of this chart, send me an email (I believe it will go as an attachment), or send me a #10 SASE, and I'll send it to you. Many people have found this chart useful. My contact information is located in my profile. Just click on my username to access the information if you are an SOR member.