[latchkey]

They do mention the issue of osmosis in the video which factors into the 10% difference as well.

The floating bag gains outside air over time since it isn't really under pressure internally. This displaces the helium in the bag and therefore, it doesn't provide as much lift. There is no way to remove the air without just emptying the bag. Which they said they do yearly.

So, like a sushi restaurant, make sure you time your visit well.