...ok, starting by the end, no? I mean, you don't meet anyone from book 2 in book 3 but Ty Lee? Or am I forgetting something?
As far as I know, until near the ending it may as well be happening concurrently?
And about Shady, even if he is not time-hopping with you and only acted snake-like on your second meeting from his perspective, from his perspective you are also a different person in each book. Thus he has no reason to worry about letting it slip that he hisses when not paying attention on book 2 and not on book 3.
The point here is that he does let it slip when you first meet on book 2.
...unless Shady in book 2 is not the same person than in book 3? Making book 3 be the actual Shady and from 2 onwards (timeline-wise) a snakey substitute - explaining his lack of aging.
You do know slave and love routes are very different? Iroh is the biggest connection but hes only in bk2 love, not slave. Ty Lee also has a bigger impact on the story in bk3 love route and they go into the story of the 3 girls more. I think love route usually gets more effort in the story side.
The Shady theorys are getting mixed up. Clearing it up theres two theories. Shady is MC that warped back and Shady is another split entity like the snakes. Also theres both hes MC and then split.
I think Shady realizes right away in each book its you, I might be wrong about that though. I think MC probably has very unique mannerisms as someone from the future and thats how hes identified so easily. The girls also know right away.
The last part is very interesting, I hadnt thought it could be different Shadys. So then Shady was body snatched? It doesnt explain how bk3 Shady also knew what you needed but maybe theres another reason for that. Maybe its not Shady that knows what you need, what if its some mysterious supplier that gives Shady what you need so it just looks like Shady knows?
Also in bk2 you know the slave girl keeps mentioning "losing time"/ blackouts? You are supposed to assume its the slave collar commands but thats a red herring, I forget if its in love or slave route (probably love) but she has been getting possessed too and helps out in the ending in the possessed state. But thats a different possession, MC swaps places so whoever it is gets his original body in the future. The slave girl just experienced nothing during that time.. unless her memories when swapped were wiped somehow.
Edit: I dont know what his hissing there would be a hint for anyway. Maybe hes trying to warn you about the snake ladies?