From Mike Mahler's "U.S. Revenue-Stamped Documents of the Civil War Era" (a must-have for any 1st issue collector). Emphasis mine:
Quote:
Bank Check EMUs are common, so much so that only those dated October or November 1862 are of much significance purely as early usages (Mahler, 1989g). However, pieces from December 1862 or early 1863 are still highly collectable, and can be significantly early for their particular origins, especially away from the cities of the Northeast. Any piece bearing a 2˘ Bank Check orange from its First Printing(s) is a good item. These stamps often have a distinct yellow tint, and were printed only from late September until about October 10 of 1862, when the color was changed to blue, reverting to orange in August 1864 (Toppan et al, 1899). Scott makes no distinction between them, but stamps from these first printings are probably fifty or a hundred times scarcer than those printed in 1864 and later. Virtually all were used by early 1863 (Mahler, 1995a, 1997).