What on earth does 'unique' even mean?
Every once in a while, someone will put a device in a circuit in such a way that "unique" characteristics not captured on the spec sheet, or subject to a wider range of tolerances than you would expect, will play a large role in the performance of the device. I've seen this most often in "sound synthesizer" type circuits (Like the Adafruit X0XB0X, where builder's go out of their way to find things like "matched pairs of ORIGINAL XXYYZZ transistors", because it turns out that when you put something else in there, it ends up sounding different.