Value of 1968 Compton's Encyclopedia?

Hi! I have an incomplete set of 1968 Compton's Encyclopedias (basically 3 eighths of the complete set), of which I own volumes 9, 10, 11, 12, 13, 14, 15, 16, and 17, of which I do not have volumes 1, 2, 3, 4, 5, 6, 7, 8, 18, 19, 20, 21, 22, 23, and 24, thus 5 eighths of it. I do not have which put that into perspective. I have 15 out of the 22 1985 World Books. So, are there any listings of the volumes I do not have? Because, I'd like to have all of the volumes.