"The old-fashioned 'closet' collectors were often successful in taking decades to build their collections without broadcasting their interests to the world. Buying an important collection or exhibit, and doing so anonymously at auction or by private treaty, is a way to save time, save money, and prevent premature exposure as a collector or exhibitor of the area until you decide the time is ripe!"
I rather doubt that many of the people who use the Scott International Volume One are "closet" collectors, but it does remind me of how the collectors whose comprehensive collections have recently come on the market seem to appear out of nowhere. I suppose dealers and auction houses are aware of them, but to their friends and neighbors they might seem like normal people. (Well perhaps not that normal!) I do recall someone mentioning vis-a-vis the Harmer-Schau private treaty collection that they remembered a secretive worldwide collector who regularly outbid all comers. This is in contrast to people like Bill Gross whose collecting proclivities are well known.