I have a collection from 1954 to present that I am looking to sell , full or individual copies , and some basic advice on value in the nat geo community .
The value of Nat Geo magazines is basically based on supply. The more there are the less they are worth. The 1950' s had 2 Million copies every month, the 60's- 2.5 million, 70's -7 million, 80's- over 10 million then it started to go down till the 2010's - 4 million. The value based on sales is $5 per issue for the 50's, $2 for the 60's , $.50 for the 70's to the point where the 80's on up are worth very little.
I hope this gives you help in deciding where to go with your collection.
that is great advice and thank you Philip. May I ask for 1900-1940s
When you talk about 1900 you are getting into serious collecting. The above link is from this site (and fellow collector Mel). It gives a more detailed evaluation of the value of the early years..
Good luck in your collecting endeavors...