I'm glad you put in that piece on the Frelinghuysen stamp collection. Concerning the 1918 Inverted Jenny stamp, there in an interesting account of it in the book The Day They Shook The Plum Tree by Arthur B. Lewis. If any of our readers have this book in their library, it can be found on pages 245 & 246.

Colonel E.H.R."Ned" Green purchased a sheet of them for $20,000 (a lot of money in those days)! He was constantly besieged by kings, maharajas, princes, and multimillionaires to sell some of them. Finally about 1930, he broke up the sheet, keeping the prime positions, including the center line block for himself. He numbered each stamp on the back, so that the buyer would know the exact position of the stamp on the sheet. The individual stamps sold as the book states, "so fast it would take your breath away". The nearest thing to this in numismatics that I can think of would be the 1955 double date cent.