Wow, thanks for all the info, guys, this forum is amazing! So, to summarize: this pennant could have been made as early as the 1940s, but most likely c. 1960, as the World Champions use of the same graphics would suggest? And these aren't repros of earlier versions, the Ad Flag Co. artists just liked using antique graphics on their modern pennants? Anyone have a guess on a range of dates during which this stiffer kind of material was used, and what's the earliest it could have been? Lastly, here is a link to Rob's Felt Football forum Packers section, and it looks to me that many of the pennants he's tagging as 1930s and 40s are made of the same material as the one I bought. He has such an amazing collection, it's hard to believe he wouldn't have a good idea of the dates of issue of just about everything in his collection. Thanks again for the help.
http://feltfootball.com/green-bay-packers/