A section of the tank wasn't blocked off...the 620 tank was missing an air release valve under the passenger seat. Without that valve an air pocket in the tank (beneath and behind the rider) would prevent the tank from filling completely.
2 things could be done...install some sort of valve, which a few people did...or ride the bike around the block after filling, which would release the air pocket and allow the tank to be filled the rest of the way. It was normal in the 620 to completely fill the tank, drive a few miles, look in the tank and not see any fuel because it all moved into the "air pocket" part of the tank. It also isn't uncommon for 620 owners to claim some insanely high MPG because they unknowingly filled it completely full once.
I have no idea why Ducati did that. It was stupid, as the valve couldn' have cost much. I guess it was just the cumulative effect of the valve, plus installation, that added up.
The air release valves on the MTS1000 models are famous for clogging/sticking...causing that bike to have a lower capacity as well.
I carried a short piece of tubing to clear it every time I fueled. That bike had character!!
