Exactly. So if I were to find a place that can be opened by the sapphire key found in Kratus's building, I still wouldn't know I found the right spot, because it's not the only sapphire key in my inventory. The same goes for lots of other types of keys.

I am in blood
Stepp'd in so far, that, should I wade no more,
Returning were as tedious as go o'er.