...from one of Bill Retskin's eBay auctions:

[From the AMCC WebSite: Matchcover flats or salesman's samples are officially not part of the matchcover collecting hobby. When the hobby began (ca. 1940), there were millions of fine matchcovers to be collected. No one wanted flats. As the industry is all but dead in the United States, salesman's samples are becoming more desirable for two specific reasons. First, they are the finest and most colorful graphic example of the design, used by salesman to influence future customer sales. Second, there are very few of them around. By definition a flat is a matchcover factory stock that never contained matches or was never machine creased or stapled. (i.e., if 20,000 match books were ordered, maybe 10-20 salesman's sample flats were produced.) Some have strikers, some don't. A few have printed strikers to give the flat more of a matchcover-like appearance. In any case, these are first run salesman's samples flats and are considered scarce.]

(Note: Matchcover flats are becoming well accepted on eBay, both by matchcover collectors and category specific collectors. Some flats have strikers, some don't. A few have printed strikers which gave the flat more of a matchcover-like appearance. In any case, these are first run salesman's samples flats and the best of the design run.)