How to use Apple TV promotional subscriptions on two purchased devices?

I have a promotional Apple+ subscription from an iPad purchase that is good until July of 2022. In the meantime I purchased a new Apple TV device on cyber-Monday that has a 90 day promotional for the subscription that has to be claimed with 90 days. Is that subscription added to the back end of the of the first subscription? If not then that subscription is essentially worthless. Anyone know how the promotion works in instances like this?