Some things I find interesting.
 Hope you also do....

Disabled American Veterans (DAV) 6¢ Franking

The 6¢ rate period began January 7, 1968 and continued through May 15, 1971.

Precisely dating is difficult as the covers are "mint" examples and do not have any cancellations.  I would very much appreciate any information/insights which could help to accurately date these covers. 

Franked with three tagged 2¢ Jeffersons (Scott 1055a, Krause-Minkus 588p1ssz) this cover has a holiday theme artwork.