Everything Ken says is true and correct. And CD disk of my book is now available for half the price of the book, which is long out of print. Go to
www.stampexpertizing.com to find a link to the available CDs. I personally chose the 15c to collect for several reasons, one of which was the fact that nothing definitive had been written about it since Brookman and to a lesser extent, DosPassos. I also liked the way cancels show so nicely. I found it to be a most attractive and interesting stamp. But my book (or CD) is very useful for anyone interested in that whole 1870-1890 period, as much of the production info on the 15c and types of existing material, is also true for the other values. There is a form on my website for ordering the CDs.