Yes, they date the passes. The CM asks when you're leaving WDW and puts that date on the card. The Ebay seller must have told the CM some story to get Oct '08 on his card.
Perhaps Universal has a better idea, a daily pass, dated for that day only.
How do I know this? The Mrs. has a critical illness and is one of the many many genuine people who get the GAC card each time.
Also.... on hearing about the GAC card a few years back, our docter gave the Mrs. a letter to take to WDW to explain she's a genuine case etc, the CM would not look at the letter saying its against state law to question a persons health ( or something like that), just goes to show how easy it can be for the knobs to obtain a card under false terms