Looks like a lot of the big walk thru sites crammed the entire story into a few 12 hr sessions and called it a day, as I've seen lots of incorrect statements from them, including omissions. Figured I'd post a few as people might be unaware they are missing out essentially on bonus content.

Before diving into a few examples, any time you read a letter in the world, OR even your mail box after a story arc alliance completion, READ IT carefully. Just because it does not update as a quest, doesn't mean it's NOT valid.

Some examples are:

1. Inbox Mail about Gaedric after finishing the Cent arc (Gaedric is part of an earlier arc, and dunno if it can be missed if doing in wrong order) IF he helped during Cent arc castle fight. Read letter in longhouse mail box after completing Cent. Even though it doesn't appear as a quest, go to Cyne Bell Castle for a hidden cut-scene. Bonus x2, IF you left Lady Eadwyn "in Gaedric's care" during earlier arc, you'll get MORE info on her and what she's been up to in the cut-scene.
2. After finishing Scriropscire arc, go back and visit Ceolwulf in (I think) Ledecestrescire. You'll get a hidden cut-scene with him (he's in the longhouse, on his throne). Also, if fast-traveling in, you'll get another hidden scene/dialog at the small mausoleum which you can enter and interact with.
3. During the Grantebridge arc, when looking for all 3 during Orphans of the Fens quest, there's a huge amount of the quest that NEVER appears as needing done, and ultimately hides a chunk of dialog options later on with Soma. So, IIRC, do this:

Talk to the people in town 1st during the investigative quest to find the traitor. Several townspeople will have dialog boxes above them. One npc will mention an abbey and the camp to west (Meldeburne and Utbech) remember this. Other will mention seeing a boat in wrong spot night of attack.

Investigate the hidden entrance to the longhouse after npc talks. It's outside the town walls. USE Odin's sight and investigate inside the tunnel AND outside. Should get an update on the footprints outside leading away, and I think somthing about yellow paint. Also, notice the X on the rock wall next to hidden entrance. Follow path/direction they're heading to the shore. Think one more Odin site at shore.

GO to the 3 locations you found each advisor AND find their boats. Each boat is on shore, close to where you found them. Each boat has a plaque on inner hull that you can read. It's meant to let you know which boat belonged to which adviser. Investigate yellow paint on the pristine boat (other 2 boats are battered w/o paint) to get an updated Eivor dialog and I believe an investigative outline of events (can't remember tbh as I fumbled though this at the time)

GO to Utbech (or the abbey if you really want to) which is closer and easier to clear. Once cleared, go inside the main hut and use Odin's Sight. You'll find a note (same note is at abbey) read it.

When at the point to chose the traitor during Stench of Treachery, the ORDER of the dialog choices MATTER. Done wrong, you'll miss extra Soma dialog. Good news, you can repeat the questions until done correctly (you'll know it's correct as Soma acknowledges and Eivor mentions the yellow paint on the boat). IIRC, 1st dialog choices with all 3, chose Galinn only options (all evidence from note, paint on boat, and alibis given by townsfolk for other 2, only point at Galinn). Go back to main dialog choices after Galinn options and select the secondary branch (I forget what it said, but it's the option other than the 3 npc). Eivor SHOULD mention yellow on the boat and the note IIRC, mentioning Gallin, and Soma will have extra dialog. If you chose the secondary dialog branch 1st, Eivor won't mention the yellow on the boat or Galinn (again, IIRC, hadn't thought about it in awhile) so you'll have to reselect the other dialog boxes until it updates the dialog with all info.

I fumbled though this as I couldn't understand WHY Eivor was failing to mention the yellow pain ON the boat AND the letter from Utbech/Abbey. But managed to get it right. All of which is essentially hidden and optional, but gives definite closure and Galinn w/o a doubt and extra Soma brownie points.

Essex Devil's Hole
Another one guides get wrong. Speak to holy guy, then enter cave and speak with Beastmaster. Do NOT kill anyone including the bear. Go west of the cave (use raven to see them if having trouble) and pull the pack of wolves to follow you to the cave entrance. Wolves will clear the npc out. Once gone, go back in the cave and you'll get the "better" dialog.

That's stuff I've found that I'm aware of as probably getting missed by many, in part due to incorrect walk-thrus missing stuff and/or the trouble I personally had during certain areas where I had to question WHY something was making sense. Hope it helps someone and remember to READ the letters and do NOT expect a quest update constantly.

I blacked out large swath of spoiler post that shows correct in edit box but NOT on screen after submitting. Another bug....