What is the special edition of Encyclopedia Britannica entitled the Constitution Edition Limited?

There is a page bound inside the PROPAEDIA Outline of Knowledge, Guide to the Britannica that says....."This special edition of Encyclopaedia Britannica entitled the Constitution Edition is limited to 49,999 Sets numbered from 1 to 49,999 This is set number ___________. They are 15th Edition, 1987.

Beautiful Blue Leather. I don't what about them is different other than the color and sets printed. I have a full set and all of the annuals up to 2005; which I think, however not positive, is the last annaul printed for the set.