Clickbank cookies?

Hello I'm a total newbie to IM, so I apologize in advance for any ignorance.

Here's my story...

I set up a website in late June promoting a clickbank product... I spent a few days making some backlinks (forum profiles, social bookmarking), and for 4 weeks my site was buried on page 10 of google results for my main keyword.

My life got busy for a few months and I had no spare time to mess around with IM.

Well, i few days ago I "checked in" on my site. To my surprise, my site is on page 1 of google in the 4th position for my main keyword. I guess i did something right and it needed a few months to get going.

That's my story, here's my question...

All my affiliate links on my website were set up with tracking ID's for Clickbank. I have made some sales, however ALL my sales are with tracking ID "not set." I have no idea how I'm getting sales on a hop with no tracking ID. The conversion rate is 50%. When someone hops to the sales page from my site, is there like a clickbank cookie sent to their computer? The only thing I can think of is that they hop to the sales page, leave, then go back and buy, and I get the credit??

Any ideas? Thanks!