It does end up being a complicated thought process for a simple effect, but I think it is also a good place to start developing solid strategies through thinking through the unavoidably complex nature of logical constructions (not that there aren't design and UI improvements to be made).
In general, I try to use a strong metaphor of locks, keys, and pins. You can see a longer version of this in the manual. When you create a lock on a trigger (or tab, etc.), you specify the key(s). Each blue box is its own key. So it doesn't matter to key 2 whether key 1 works. Any key works fine.
Within each box (or key) I think of each statement as a pin. For a key to work, each pin needs to work. All the statements have to be TRUE. If there is one bad pin, the key breaks and the lock snaps shut.
For the specific instance, or any specific instance, I walk through each pin at the various stages of the game to see if the lock will be open or closed:
At the beginning, when the player has done nothing, is this statement true, is this one, etc.
After the player sees this plaque, what changes? In this case, the statement about having viewed a plaque goes from TRUE to FALSE. When it is TRUE, the key (or that part of it) works and the lock is open. When the statement becomes false, the key breaks and the lock snaps shut.
Hope this helps. I'd be happy to hear others' strategies too.