My searching of ProQuest that started a year ago is now filtered down to 79 references.

I am attempting to find the 20 classic references to the problem of Knowledge Loss. I may have nine or ten references now and these are books. I should be adding peer reviewed journals. I should cut some of these books and add more journal articles. I have only one or two classic knowledge management books and these two I will keep. And I have two methods books. And I have two knowledge loss books. I am looking right now at the possibility of narrowing down the 79 present references. I also now have the idea that I should perform a search on ProQuest and Google scholar for the term Knowledge Loss and find about 15 papers that way. After all, the previous searching that is now narrowed to 79 papers, was about searching for ways to measure knowledge. What I really need is papers on the main topic: Knowledge loss. Also I think ten books is too many books. So I will cut the book list to the six books mentioned above and cut the previous search to five or so papers then find ten or so peer reviewed papers on Knowledge Loss.