Help me on a piece of music's art history....


I recently and for reasons not known to me stopped into a small antique store while on vacation.....I saw a poster that caught my eye. It was the billboard poster for the 1972 Watkins Glenn '' Summer Jam'' concert that featured three of my all time favorite artists ; The Grateful Dead, The Allman Brothers Band and The Band....it ended up being larger in population than Woodstock. It is in great to mint shape and I am 98% sure this is not just a recent reproduction but very well could be the first run of this poster. I went on the Internet and saw where the promotor of these bands the late Billy Graham, ( I do believe the site was called Wolfgang Productions ) had one which is probably the original and it was NOT FOR SALE !!! He had other concert posters from ''that era '' for sale on that site. This could be and I am hoping that this is the first run of these posters used for the promation of that concert. I was almost 16 and had my backs packed to go along with my brother and his friends and my mom stopped that from ever happening...NO it is not for sale but does anybody have an idea of it's worth or who would possibly know if this is in fact the real deal....!!!!
garebear
Saturday July 28, 1973 to be exact. The promoters were Shelly Finkel and Jim Koplik. It was called Summer Jam.
Crowd estimates were between 500,000 and 650,000 depending on the source. I was there and it was a wild weekend. We arrived on Thursday evening and by then they had pretty much given up on collecting tickets. As a result, I still have my entire 10.00 ticket. Friday late afternoon/evening, the Grateful Dead's soundcheck was about 90 minutes long. I have the tapes from it and listen to them often. There were rumors of a movie and soundtrack album to be released but it never came to fruition. Too bad too. There was some remarkable music that weekend, including a monumental "Mountain Jam" featuring the Allmans and the Dead. Of course the obligatory torrential rain on Saturday afternoon as well, creating a lot of mud. If the Finkel/Koplik boys are not mentioned on the poster, it's a phoney. If the date on it is 1972, well, that's a dead givaway (pun intended).
As a followup, if, as a re-read your correction to the date, it has Finkel and Koplik on it and is the real deal, my guess of a rough estimate of worth is 275.00 - 400.00. If it is a mint first run maybe more. There was not a whole lot of memorabilia spewed from this show, including photos. As my previous post indicated, the most numerous stuff is intact tickets. I can't recall seeing many posters around, though I have seen some repros. I hope you grabbed it. If not, where is the store? ;)