Word of God: A Q&A from the Japanese Path of Radiance website gives the average lifespan of each type of laguz. 5-6 times the beorc average for the beasts, ten times the beorc average for the hawks and ravens, a thousand years for the herons, and two thousand years for the dragons.
Fire Emblem: Radiant Dawn[]
Acclaimed Flop: The game did fairly well in the review circuit, but it's one of the lowest-selling Fire Emblem titles ever, even setting aside the small print run. This is the game that first put Fire Emblem on the cancellation brink that Fire Emblem Awakening would reverse five years later.
I Knew It!: The Black Knight's true identity of Zelgius, as well as Bertram being a Brainwashed and Crazy Renning. Thanks to the magic of hacking Path of Radiance and examining unused files and dummy data, many saw these coming a mile away, although Ranulf spoils the former in Radiant Dawn for those who didn't.
Urban Legend of Zelda: Rumors of additional support paired endings in Radiant Dawn such as Stefan/Soren, Meg/Zihark and Micaiah/Pelleas abound. Serenes Forest has confirmed they never existed.
Unused dialogue suggests it was once possible to spare Hetzel's life in the final chapter, which is a But Thou Must!Kill'Em All objective.
Unseen data shows that Levail has his own growth rates rather than using the defaults for his class, suggesting that he may have been recruitable at one point in time.
Word of God: Information (that isn't even officially translated!) gives the backstory of the Dawn Brigade.