It's clearly mathematically possible, just consider a case where 8 NFC teams are 12-4 and the other 8 are 4-12. That's an extreme example but it will serve as a proof. But we don't have to see such extreme numbers to make it possible, not when you consider that 2 division winners can get in with records worse than 12-4, conceivably even losing records. In such a case, there would only need to be 5 teams at 12-4 or better to keep one out.