They aren't proper abbreviations, and some leave them out altogether. I lowercase them to prevent them from distracting people and making them take another second to figure out which book I am referring to. I seldom think about the articles in the titles and only acknowledge them to be precise. If we're going to be persnickity about grammer rules, shouldn't the abbreviations be punctuated?

As for the real issue, it doesn't seem that hard to figure out. IIRC, she kept them in her room. You go into her room, find the likely hiding places for a bulky collar & bracelet set-up, and it should be fairly quick. I think her protections were basically like a safe, rather than a hiding place. Protect it so well it doesn't matter if they can find it. In this case, Semirhage was equal to the task of cracking the safe.