I suspect (experts required here) that a form of 'phase cancellation' may come into play if going quickly from A to B if both have common elements.
e.g. if A has a slug of, let's say immortelle, and B also has immortelle, then after smelling A . . . B may seem weaker (or at least the immortelle note not as strong) and the other notes may be more apparent because the nose has just had a blast of immortelle in A and become accustomed to it, or at least slightly de-sensitized to that note, and doesn't notice it as strongly in B as one would if smelling B 'cold' so to speak, with a fresh nose.
At least that would be my assumption, so in the rare cases I do an A & B (as I did with two different batches of Santal Noble recently) I would take a bit of time between each . . .
No scientific basis for this - just a hunch.
PS To answer the question, though, I think half the fun of all this is in comparing and contrasting different scents and different perfumers variations on a theme etc. - that's how I learn . . .