Scott 423C is a candidate for
fakery, since it is relatively easy to manufacture by reperforating two sides of a
428.
However, the compound perf stamp is so rare that a fake would hardly escape detection.
The Chesapeake Collection of U.S. 1914 Compound Perforations,
June
12, 2004, Robert A. Siegel Auction Galleries Sale
877 is an important reference auction catalog and includes a large
collection of these 1914 compound perf stamps, as well as an
illustrated census of each. Note that the 1914 compound
perforations were "elevated" by Scott from error status
to major number status in 2003, meaning that they are now
considered regular production stamps, albeit exceptionally rare,
and not error stamps.
