I think the FFO dialogue contained something about memory loss, but I'm not entirely sure. Certainly, the NES version doesn't mention it, but I have a feeling FFO does.

If Garland is sent to the future by the fiends, he's probably sent back a good few years before the light warriors appear. Although it's unclear, I think the fiends can send Garland back at any time period, in which case he'd probably be sent back a decade or so before the light warriors appear. In my opinion, being 'defeated' once every ten years is a small price to pay for eternal life.