Even though I am a 25+ year member of the American Philatelic Society, I missed the 2009 article in the APS journal titled "Selling Stamps Can Increase Your Collection" by Forrest H. Blanding. Fortunately, friend of the blog ChrisW was more diligent and has recently written about the article on two stamp collection discussion forums. While much of Blanding's article is devoted to how he leveraged selling stamps as a dealer to support his collecting (usually thought of as a "no no" unless you collect in an area other than what you sell), I'm going to concentrate on the details of his collection.
By the the time the author finished high school, he already had "25,000 different stamps in Scott 19th Century, 1900–1919, and 1920–1926 international albums." After a time out during college and early marriage (sound familiar?), he started purchasing in earnest, buying thousands of collections over a 50 year period which he resold largely via approvals or wantlists after removing what he needed. The end result?
"My collection included issues only to 1975, because accumulating the massive wallpaper being issued after then took too much time, cost too much money, and did not provide any real collecting challenge. The final collection included 98 percent of all major world stamps listed up to 1975 in the Scott Catalogues — more than 200,000 different stamps, all in mint or unused condition except for some high-priced nineteenth-century issues. It filled to near completion fifty bulging volumes of the Scott International series. It included the best copies from all the collections I had purchased over the years, so the stamp condition was usually exceptional on all but some of the early values.
Two-thirds of the Scott-listed countries were complete in major varieties up to 1975, including some larger countries such as Denmark and Norway. Germany proper lacked only one stamp, France lacked two, and Canada was missing just three. I could never have owned most of these stamps with-out my collecting-selling activities."
(I'm assuming from Blanding's description that he vastly expanded the International Volume One or more likely used the original Browns.)
When Blanding decided to sell his collection in 1995, he did so through his own dealership and auction houses.
The article, by the way, appeared in the November 2009
American Philatelist on pages 1044-1048. Well worth a read if you have access.
So we now know of three collections 98+% complete for the periods 1840-1975, 1840-1981, and 1840-2012. I have to believe there must be more. In fact, I just added a couple of additional possibilities to the list (Cole and Johnson).