Scott's listing format of 668, 680-83 and 688 implies that these issues were printed in se-tenant format only. This is incorre

Scott's listing format of 668, 680-83 and 688 implies that these issues were printed in se-tenant format only. This is incorrect. There were actually two printings of each issue: one in which each denomination was printed separately and a second printing (in smaller quantities) in which each issue was printed in se-tenant format. Thus, se-tenant items command a premium over separate single stamps. One can be assured of the separate printing issue by collecting those stamps in horizontal pairs which exist only in the singles printings.