There are various cachets in this listing, including printed cachets, rubber stamp cachets, official NASA cachets, etc. All covers are unaddressed unless otherwise noted.
All commemorative covers are for launches unless otherwise noted.
Hence the official NASA cachets on these covers for the Viking launches are marked Viking A. Other cachet makers have also followed NASA's lead in some cases. When describing a cachet, I describe it as shown on the cachet. A purple rubber stamp cachet. This double cancel cover is scarce, only a few prepared this way with the Official NASA cachet. A purple rubber stamp cachet, Kennedy Space Center FL pictorial space slogan machine cancel on space stamp.