Now that we've seen Will in Oz, this means there's more to his tale than we thought, not just about the events after the spin-off.
Born in Oz (most likely), Penelope died, he met Robin and drank the elixir, and he figured out a way to get to the Enchated Forest (maybe the same way Zelena traveled to the EF before the events of New York City Serenade).
He came to Sherwood Forest and met Marian and the rest of the Merry Men, met Ana and fell in love with her. Will joins the Merry Men and steals the magic mirror to go to Wonderland.
Will and Ana are struggling, Ana marries the Red King and Cora takes Will's heart. Will becomes the Knave of Hearts. Alice gets his heart back, they parts ways and he becomes a Collector and meets the Lizard.
Will leaves Wonderland to the Enchanted Forest (I think this because Lizard said that people think Will left because of his debts. They would only say this if they knew he left, and if he was in Wonderland when the Dark Curse was cast, then they would have been frozen in time while he and Jefferson were being taken by the curse).
He is taken to Storybrooke by the curse but retains his memories (he said in 4x07 that he knew that time stood still for 28 years, but everyone else was oblivious to it. The curse broke and he was taken to Wonderland by the White Rabbit.
The events of OUaTiW happen. I think Will was most likely take back to Oz (if he was born there) when Regina cast her spell in 3x11 (Regina said that the spell would send everyone back to where they are from).
So either Will spent a year in Oz or the Enchanted Forest and was then sent back to Storybrooke because of Snow's curse before he could reunite with Ana.Â
Anything I'm missing?