I'm overwhelmed by the response to my query. Thanks to everyone who has chimed in. I like the idea of going chronologically so I ordered Plenty of Blame to Go Around.
I live in the Dallas area and get the opportunity to visit several different Half Price Books stores including the flagship store in Dallas which is huge. It has several bookshelves filled with Civil War tomes. A big portion of my library has been purchased through Half Price Books. You can find great deals. Plus, as my wife would say "I love the hunt as much as reading the books." True. I went to a couple of the smaller stores nearer me this morning. Lo and behold I came across Mr. Wittenberg's Little Phil, so I had to pick it up. It is the first Wittenberg title I have run across during all my visits.
I have learned a few things from the many hours and visits to Half Price Books. There are certain titles and authors that you can find at every store. Some of that is due to the shear volumes printed. However, there are some titles and/or authors you rarely, if ever, come across. Eric Wittenberg is one of those you rarely, if ever, see. One of things I have learned is that there are certain authors and/or titles that folks just do not sell off out of their library. It appears that Mr. Wittenberg is one of those authors. It seems that once a person adds one of his titles to their library, they do not let it go.