I've recently got back into Smash and remembered I never downloaded the Piranha Plant DLC, so I dug my email out and saw it says download by June 30th 2019 on the email
So anyone like me who bought the game around launch and got a DLC code, you have until Sunday 30th June to claim it
Thank you for purchasing Super Smash Bros. Ultimate. As a bonus for purchasing the game early, we are sending you a download code for the new fighter: Piranha Plant, which will be playable from around February 2019.
Redeem your bonus download code now to play as Piranha Plant as soon as it becomes available.
This download code is valid until 30th June 2019.
So anyone like me who bought the game around launch and got a DLC code, you have until Sunday 30th June to claim it