There may be conflicting information, and different things printed on different credentials. The credential I just received today says "You must obtain at least one sello every day, dated to validate your journey. Those on foot, horseback or wheelchairs must collect two sellos per day during the last 100 km; cyclists two per day during the last 200 km."
No one is denying that some people, including some volunteers at the pilgrim office share your opinion. The question is, do you want to send someone to the office, having walked for week after week just collecting one stamp, trusting what you wrote above, only to find that the particular volunteer they end up in front of doesn't share your opinion and they are refused a Compostela? It has happened to pilgrims who have reported the experience in these forums. It may not happen often, but it does. Is it something you want to advise a pilgrim, for whom the Compostela may be very important, to risk?