I have inherited
a couple of boxes of first day covers and am now getting time to inventory and evaluate the lot. There are several hundred US covers from the late 20s to the early 80s, the bulk in the middle. Most appear to be in excellent condition with a lot of ArtCraft cachets. My question is about organizing them for sale. I started grouping by cancellation date but quickly fell back on Scott#. That runs into complications where the same stamp, a 4c July 4th 1960 flag for instance, is used on multiple covers over multiple years (USS Sargo, USS Saratoga, etc). Then there are the UN stamps, UN Airmail stamps and regular airmail stamps.
Lots of intro for a basic question but what is the preferred method to organize covers?