Alphonse Mucha Poster

My grandma purchased this poster at a garage sale in the 80's. She was familiar with this artist and purchased the poster for $1.00. She has kept it in her closet rolled up in a cardboard container. My sister, cousin and I are all needing extra money to help get us through college, so she gave it to me thinking it was a lithograph. She wanted me to research it, sell it and split the money with my sister and cousin. I took it to an art dealer in Portland, OR and there she informed me that the lithograph is actually a poster and would only be worth a few hundred dollars. I understand that a lithograph of this particular picture can be worth up to $2,500-$3,500.
The poster is in decent condition. There are a few push-pin holes in each of the corners. The color is good.
I've tried to research on the internet about this poster but can't find any information about it. I would like to find out approximatley what year the poster was printed and what the value of the poster would be. Also, how I would distinguish this poster from an original lithograph? In one of the pictures, it says who and where the poster was printed. I can't find anything about the particular company and there is no date on the poster anywhere. Thank you!