I don't know lots about this so I won't pretend like I do But, I assume it is the same as any ingredient. You can read "rose" or "iris" or "sandalwood" in fragrances notes and it can smell completely different in each one.
Obviously there's the rich "Catholic" incense (as people call it), you have more Arabian style uses etc. I'm also assuming it's down to what it's blended with also. For example, a rose would smell different if you added cocoa to it, to if you added bergamot. Oils interract.