Do not rely on later activation to recover messages that Polymorfa did not retain. Storage settings govern the eligible data captured while enabled; they are not a backup of every conversation that already exists on a phone.
Before changing the setting, identify the period you need and whether your project has eligible history access. Keep any evidence you already lawfully hold in your own system. If stored messages from an enabled period are missing, support can investigate that specific range. There is no basis to promise recovery of unretained content.