A pretty good compromise for this is "first cookie opt-in, last-cookie sales".

This system allows you to reward affiliates for leads (whoever refers the lead first gets the reward - that can be a per-lead fee or prizes from opt-in contests), as well as sales.

When you take away "last cookie" from the sale, you remove one of the biggest momentum plays for a launch: The benefit of the affiliates to offer bonuses.

Another aspect: Once the cart is open in a launch, you typically don't capture leads. Instead, every time a prospects enters the launch through an affiliate link, the cookie is reset in favor of that affiliate. Without that, there is no incentive for any affiliate to mail after the cart is open.

And: As soon as a niche is fairly established, there is huge overlap between the lists of the different affiliates. So it's not like if you don't mail to your list everybody who is on your list will never hear about the launch.

Because of that, there are two competitive angles for the affiliates in a launch: 1. who can send most leads FIRST, and 2. who can make most sales (whoever got that prospect to FINALLY buy - either through a bonus or just by sending that extra email that pushed them over the edge - deserves that credit)

And these competitive angles are matched by "first cookie opt-in" and "last cookie sale".

BTW: You CAN have total control over that - even with 1SC and Infusionsoft. In a recent six-figure internal launch in the real estate niche that I managed, we captured the affiliate code into the record for each lead. That enabled us to mail out AFFILIATE LINKS to the launch list with an early bird notification. So we reset the cookies in favor of who sent the lead first - just before the cart opened.

Hope this helps!