Let's say customer C, visits blog B and clicks on a product from shop S, putting it in her cart. The affiliate network registers that for customer C, a future sale that customer C will complete from shop S, will be attributed to affiliate B. But if now, C goes to, say, YouTube channel Y and clicks on any product pointing to shop S (the same shop), the network will now register Y as the affiliate to attribute the sale to, even if the customer had placed the product on the cart, through B's blog.
This happens on the click of a product, so to be sure you get the commission, the person that does the sale, must not click around on other people's blogs until she completes the purchase.
Of course that works the other way around. If someone puts all her desired products in her card through Y's youtube channel and then pops up in your blog and clicks on at least one of your links, any and every sale will be attributed to you. No need to put anything in the cart through your lists, just to click!
The 30-day cookie attribution that networks refer to, is valid, providing that nobody else steps on your cookie, replacing it with their own.