As of now, Forever Saves on your presave only apply to your latest release, and all future releases, and do not work for your past releases retroactively.

In the near future, we may roll this feature out - however, we want to make sure we make it easy for fans to consent to which songs they want to save, and adding an appropriate flow for fans is important for us.

Regardless, as you continue gaining more saves over time, every release you drop in the future will benefit from the additional saves + streams.