You might have unmatched pairs in drawers somewhere? I would look again at the pairs that have supposedly been "matched" up. This might reduce the odd socks a bit. Then look in silly places, like behind the fridge, did someone take their wet socks off and put them on top of the fridge? ditto freezer, and tumble drier.
I have a misbehaving teenager in this house. He comes and goes at any hour of the day or night, demands food, without a please or thank you. Sleeps wherever he wants, never tidies up or helps out. Fortunately he is only 15 inches tall, has a white fluffy coat, and a very long white fluffy tail.