the ratio of the carmelized sugars, dextrines, lactose, and maltose is going to be changed by the ration of the specialty malts.
That change in ration carries through to the runoff. What does not result in the sparge is not because it did not convert, but rather because it was not rinsed free from the grain.
Yes, in the same nature you really are just steeping, but steeping grains do not result 100% in the boil as the sugars adhere to the kernel.
That "some" that you speak of continues to remain in ratio with the rest.