Originally Posted by
rittenhousesq
The official entry requirements for the lounge state a same day ticket in Acela first class (if that's the criteria you are using for entrance). It's not specifically a departure lounge, so you should be able to use it when you arrive.
Lounge access is allow for all Select Plus members.
Select Plus Benefits | Amtrak Guest Rewards
So Acela FC ticket is not necessary.