Short question: How did Casandalee get to the Command and Astrogation Decks without going through the Security Deck?
Expanded Reasoning: I assume that Casandalee is able to draw maps for the PCs of several decks in the Silver Mount because she visited them as an android, years ago. I likewise assume that she cannot draw the Security Deck because she never visited it (perhaps because Unity and Bastion were still repairing the damage it took in the mutiny/crash). But since the Security Deck appears to be the only way to enter the Command Deck (a sensible precaution on the builders' part), how did Casandalee get there?
On a related note, Casandalee can tell the PCs that they need to defeat Becrux, but how does she know about Becrux?