Just at nitpick..Tiger was culled by LNT, not WNT
The reason she gets saved has already been stated, when she collides with Royal Sovereign she damages the RS so badly that she is declared at loss(part from the guns,which could be used for something else...)
So when WNT comes around she is saved as per OTL and when LNT comes around she is also spared because otherwise RN would be a down a ship.
It also means she gets(slightly) higher priority
Touché. Thanks for the correction.