Originally Posted by channa

If he bought them all from one carrier, he'd still be using the coupons in numerical order.

Ticket 1, Coupon 1
Ticket 2, Coupon 1
Ticket 1, Coupon 2
Ticket 2, Coupon 2

If you couldn't start a new ticket while another ticket were in progress, any end-on-end, or trip within a trip would be a violation. And typically those are fine.

The key is if he's buying tickets to circumvent the minimum stay requirement, which he technically is, but with two different carriers, it makes it difficult to prove and questionable to enforce.

In this market, I would double check to make sure there truly is a minimum stay, or if you're just running into an availability issue that only works right on these flights. It's possible these are one-way fares, as many in this market are. If they're one ways, there is absolutely no concern about a violation, since there's no min stay to violate.