We have posted a few times without any replies for our issues of National Geo years 60's and 70's. Even though most include supplements & maps, as well as, issues with the Coca Cola Ads. We also noticed that sales from other members are extremely rare. Should we attempt to sell on Ebay or just give the issues to schools for tax write off purposes?
Have you reviewed this?
It doesn't answer your question directly - but gives insight as to the value of your collection and as to the possible methods you might be able to market it.