Suppose I have a ticket for a flight that I want to take, and a ticket for positioning flights. The tickets are on different carriers (on different ticket stock), but on the same PNR.

So I have one ticket that's AAA-BBB round trip, and another ticket that's BBB-CCC round trip. The chronological ordering of the coupons is AAA-BBB-CCC-BBB-AAA. Again, AAA-BBB is on different ticket stock than BBB-CCC.

What are the effects of having the two tickets on the same PNR?

Do I get misconnect protection? (my understanding is, no)
Are the change/cancellation policies changed (ie, are the most restrictive policies inherited across tickets? My understanding is no)

If my understanding is correct -- is there any effect to having them on the same PNR? In particular, is there any benefit? Is it just so that if there are IRROPS, the carrier can see the other ticket, so they can try to route me in a way that makes sense?