When 138 was released, shingeki.net updated their "story" tab to show that the 138 "See you later, Eren" scene, was a prologue to the entire story. It happened before chapter 1. Which proves that the cabin timeline was indeed the first timeline.
If you scroll down slowly, it will show "See you later, Eren" as the prologue before chapter 1.
Timelines in order:
Cabin timeline = T1
Manga timeline = T2
Anime timeline = T3
Eren has restarted twice so far. The anime is the final timeline. If people are wondering how this is even possible, I'll explain here. Lets start off with timeline 1. In this timeline, Eren ran off with Mikasa. We call this timeline, the cabin timeline.
In T1, Eren died from the Curse of Ymir while sitting up on a bench with his back to the cabin. The last thing he saw before waking up in T2 was "See you later, Eren". Notice how he is sitting up against the tree like he was sat on the bench and Mikasa is the one waking him up.
Eren can't remember what his "dream" was about, but he remembers seeing that Mikasa's hair was shorter, and so he asks her when did her hair get so long. Also look at the cross on the tree. It marks his grave from timeline 1 where he died sitting up against the cabin.
So the cabin timeline was a failed timeline. He restarts at the tree, and now we fast forward all the way to 139 where he dies in the second timeline. Take note of where his head was buried. The grave is on the ground this time, next to the tree.
Since the tree in the extra pages grew that large like Ymir's tree, it's evident that the parasite remained in Eren's head and Eren was still alive in paths. He thought he had succeeded until Paradis was carpet bombed by B2 bombers. That's when he chose to restart again.
So after he dies and restarts, he wakes up in the anime timeline, the final timeline. Since we know Eren saw previous timeline memories of "See you later" before he woke up in the manga, we have to apply that in the anime, he's seeing previous memories of the manga timeline.
The nightmare he sees before waking up in the anime shows many things. Titans invading, his people dying, a statue with its head cut off, and his mom being eaten. People thought "It showed his mom getting eaten so its future memories". But they are actually past timeline memories
I counted the birds in the final extra page, there's 11 black birds. Usually there would be 13 birds, just like My War OP and the Blu-ray posters showed. 2 birds are missing and they are found in episode 1 of the anime right after Eren wakes up from his nightmare.
For the anime, Eren doesn't get woken up by Mikasa like what happened in the manga. The nightmare wakes him up. And if you notice as well, he wakes up laying down in a position where his head is exactly where it was buried in the manga timeline in 139.
In the anime, he doesn't ask Mikasa when her hair got so long, he just sees the dream, wakes up in fear, tells Mikasa he had a long dream that he can't remember and is shown crying.
In Shock ED and The Devil's Child ED, I've already analyzed them both, explaining how manga timeline Eren was trying to send a message to anime Eren. The phoenix's are used for that message. It's basically trying to remind himself "If you don't do this, you will fail once again."
The anime is the final timeline. Advance towards the truth.
Interesting how the cover for "The Devil's Child" is of a grey coloured eye. Manga timeline Eren is the one with grey eyes. This song cover being a grey eye is proof that manga timeline Eren is indeed relevant and is showing anime timeline Eren this as proof that he was here.
Something is missing in the lyrics of this song. She actually says something in the song right after saying "I..." at the very end, but its not included in the official transcript for the lyrics. I wonder why her final word before dying wasn't added in🧐I'll post them below 👇
"No matter what I must sacrifice, I will always be there to protect you. Even if I'm making a mistake, I don't doubt myself at all. What's right, is truly believing in myself until the end."
- The Devil's Child ED lyrics
"This is a song that sounds just like the lyrics. The future is cruelly up to you. It is not something that can be left to others."
- Sohei Mishima (cinema staff's bassist) description on new AOT themed album song, "Undersea".
"Someone who can't sacrifice anything, can never change anything."
- Armin speaking to Eren in anime original scene from S1
"I know... That's why I failed. I clung to my companions and my ties to them, and I failed."