You can also use that to know at what point you are in the timeline. Also, the train station employees go on a strike at some point in time. There seems to be, for instance, a love affaire going on in the game between a man and 2 women (what a bastard). You can watch that story unfold as you advance through the game, and that helps you know what moment you are in in the game. There are many clues to help you figure out when in the timeline is a scene happening.
The only clues I had were in-game cutscenes, dialogues (with NPCs and main characters).
I don’t know if Sega has issued an official storyline for the game and I haven’t read the manual for clues. I should mention this right now: there ARE plot holes in the game, even though the storyline is pretty consistent overall. The following timeline is nothing official, it’s just my best attempt at trying to fit everything into one coherent storyline. I then looked up the Wikipedia page, and noticed that the “plot” section was really superficial and didn’t seem correct. I found it quite telling that someone like Johnny, who’s so passionate about the Sonic series, and seems to know so much about the games (this applies to all of the BrainScratchComms crew though), didn’t really fully grasp the story of Sonic Adventure. And that’s for a reason: unless you sit down with a pen and paper (or Microsoft’s notepad if you’re like me) and try to write down as much info as you can while playing, I don’t think you can grasp the whole story – even after beating the game multiple times (which I’m sure Johnny certainly did). In another video (from the BrainScratchComms playthrough), he got things completely wrong about when Knuckles follows Gamma to the Egg Carrier. Unsurprisingly, he said the story looked coherent when you played some character’s story, but when you try to piece it all together, it’s a mess. This statement definitely has some truth in it. Upon finishing this timeline, I went back to Somecallmejohnny’s review of the game, to see how he explains the timeline. While the process did turn out to be fun, piecing everything back together was not as simple as it sounds.
I was somewhat confused by how the story unfolds, and since I like investigating and coming up with theories to explain sets of facts – and since I have lots of free time too – I thought it would be fun to write down every character’s story and then try to rebuild the whole Sonic Adventure storyline as a timeline. I still think it might have been a somewhat decent game back in 1998 – and it was certainly exciting for Sonic fans back then, but overall I think the game was somewhat underwhelming, for several reasons that I may or may not address in the future. So I’ve just beaten Sonic Adventure DX for the second time, and my opinion hasn’t really changed much. Warning: Let no one ignorant of Sonic Adventure enter here