True, but they don't tend to forget the last notable plague or ailment that befell their land. For example, in TWW, they still remembered the events of OoT (and only OoT). In LA, they still remembered the events of ALttP (and only ALttP). In AoL, they still remembered the events of LoZ (and only LoZ, well, plus Impa's knowledge of the King of Hyrule/sleeping Zelda stuff).

We don't have any other games where the people of Hyrule remember something bad that happened in the past, but don't seem to remember something bad that happened more immediately in their past, as would be the case with FS -> OoT -> TP -> FSA.

But as already mentioned, Ganondorf still invaded Hyrule in the child timeline and was known all over the land as a demon thief and evil magic-user. The evil things he would have had to have done to gain that kind of popularity before being caught have to be pretty numerous or of great scale. And if the people of FSA can remember the Dark Tribe invading Hyrule some time before the events of FS, surely they could remember Ganondorf invading as well, especially since that would have taken place much closer to the present.

Well, we really don't know which direction is absolute north in those games, but, yes, the kingdom of Hyrule during FSA exists relative south of Death Mountain, but I'm of the mind that it exists relative north of Death Mountain during the events of FS. I don't think we're seeing the same area of land in both games, particularly since FS's geography looks like the backside of Hyrule that Death Mountain is mostly obscuring on FSA's map, and the fact that Zelda tells Link that the shrine of the Four Sword is so far away and secluded from Hyrule Castle that she has to teleport them there (and then we never see the shrine in any of the area of Hyrule that is relative south of Death Mountain in FSA, which would fit the shrine being relative north of Death Mountain during FSA and relative south of Death Mountain during FS).