I have a theory about the presence of elves (and maybe shapeshifters) in various locations. In AP, the elves are only found in Venwood, near the entrance to Faiara. In Av1, you find a book in Mysten Far that explains why the entrance to the dreamrealm is now there instead of Faiara like in AP; it mentions that the entrance was moved to Mysten Far after Ahriman's forces took control of Faiara. Seeing as the entrance to Faiara was near Venwood, it seems likely that Ahriman probably took control of Venwood as well. The surviving elves escaped to various places.
In Av1, you find elves that have settled in the Oldwoods, as well as dark elves that live underground in the Rootwell. I think the dark elves may have originally moved underground in order to hide should Ahriman attack again.
Some other elves escape and later founded Verashima, while others escaped to a pocket dimension known as the Vale, where they remained isolated for centuries. You will find in Av2 that the elves of the Vale have a greatly exaggerated concept of the danger in the Land of Man, as Ean is able to survive when he leaves the Vale; however, this sense of danger makes sense if the elves who first settled the Vale were refugees from a kingdom being ransacked by demons. As they were afraid to leave the Vale, they did not find out that the demons had been defeated and probably thought that the other elves had been killed off. You will notice that Ean is genuinely surprised to find the settlement of elves in Verashima.
By the time of Av3, Ahriman has long been defeated, and many of the elves have returned to Venwood. However, when you need the key to Faiara, the queen is much more reluctant to give it to you, as the last intruders to enter were demons who conquered it. (The Mirror Caves may be the remnant of demonic power tainting Faiara.)
In TLO, you find the village of Harakauna, which is populated by shapeshifters and talking animals, and maintains contact with the Elder Oak. It may have originally been settled by changeling elves alongside refugees from Animalville. (It is possibly the same Elder Oak, as in Av2, the Elder Oak was shown to exist in two places at once.) Even after Ahriman was defeated, they may have felt a loyalty to the society they had created and decided to remain.
In Av4, there is the elven town of Delamere, where the inhabitants have tried to forget the past for fear of unleashing ancient evils. Their settlement may have been so far out that the elves in other locations were unaware of their existence. Having tried so hard to forget their past, they may have been completely unaware of their ancestors' Venwoodian heritage, as well as Venwood's existence. However, being as far out as Delamere's elves were, even if they remembered Venwood's existence, none of the elves of Venwood would be able to find them to tell them that it was safe to return home.
Edit: I previously posted this on the Aveyond subreddit.