I am a collector of Football from World CUP, European CUP and Olympics.
I browse often through Ebay and I can say without any doubt that most of the balls offered as the genuine article is most often a recent production (official or not?) that has many diferences frorm the real ball.
Some useful tips to recognize a genuine ball: (old Ball)
Adidas Tango Spain
Has Adidas on the logo and said made in Spain beneath. No leaf in the logo.
Below Tango it says Espanha, France or Germany in smaller lettering.
Says in English only Official World Cup Ball 1982
Logo = Leaf and adidas beneath (and beneather in smaller lettering the country where it was manufactured)
Says in French and English Official World Cup Ball 1986
Logo = Adidas only and beneath Made in...
Official Match Ball of the Fifa World Cup 1994 (english only)
Teamgeist Berlin (Italy vs France)
The exact number of manufactured ball worldwide is 1600
Germany - Costa Rica ( I still don't know how many)
One Detail for the collectors: Considering Adidas has manufactured millions of White and Gold balls to sell worldwide, to own one of this limited balls can reach 500 USD to 1000 USD in 2006. Next year who knows....
Whenever I have more tips on my other balls and if I feel the guide is being useful, I´ll get back to improve and review it. In the meantime beware of official replicas, unless you like replicas and post production.
There is nothing like the oldies!