Originally Posted by JJeffrey

Yes it has been like this for years now, hence all the rush last summer at the end of July to book trips with SWU's that were expiring on 7/31.

As long as one segment clears then the SWU is pulled and attached to your PNR and won't go away after the expiration date. So even if you can't find confirmed space on the longhaul flight, you can always use the SWU on the domestic connecting flight then waitlist the longhaul to keep the SWU 'alive'.