Missing three chests in Miraz's Castle Infiltration

[Wes Ide]

Hi all.

I am 13/16 chests in Miraz's Castle Infiltration and think I know which ones they are, but am not sure how to access them.

I've got all the chests in the following missions/levels:
- Defeat the Castle Guards (2/2)
- Sentries on the Turrets (3/3)
- Rescue Cornelius From The Dungeons (3/3)
- Rescue Edmund and Trumpkin (2/2)
- Break into Miraz's Chamber (no prompt to tell me how many keys I got there but I did get 2 in this area though: one behind a painting and another near the turn-wheel piece).
- I also got one near a puzzle piece on the floor just before entering "Sentries on the Turrets"

That's my 13.

Looking at the Chest Locations guide, it looks like I missed the first three chests of Miraz's Castle Infiltration.

#1 starts out with At the start of the level, you will create some steps. After doing so, you have a choice of two paths. I chose the one where you shoot both of the targets above a door...

Well, no I don't. When I start Miraz's Castle Infiltration via the level select screen, I start in a lower courtyard with stairs to climb that take me to an upper level where I have three doorways to choose from around the upper courtyard.

So how do I get back to the actual start of this level that is referenced in the Guide?