Standby SWU upgrades on continuing flights
For example:
If I am flying IAD-FRA on UA or LH standby with a UA SWU, is that SWU still good for a standby upgrade FRA-LED?
And on the return, can I use an SWU to successfully standby on LH LED-FRA, and then use that same SWU for a pre-assigned upgrade seat on UA for FRA-IAD?