I've made a down mummy bag, so I'm familiar with the construction. If the down shifted from head to foot (assuming the baffles run side-to-side across the bag) it means that the baffles have either come loose where they're stitched to the shell, or the baffles (usually a mesh fabric) themselves have torn. This can happen if the down gets soggy wet and the bag is handled without supporting it from underneath. This is why you have to handle it carefully when washing a bag.

Re-stitching the baffles could be quite a chore if the tearing is extensive. It sounds like you might have made it work, though.

Many, if not most, bags don't have a side block baffle. This allows you to shift more or less down to the top of the bag, making it warmer or cooler, assuming you don't turn the bag with you when you sleep in it.

I'm surprised it weighed 4.4lbs. new. That's very heavy for a down bag unless maybe it's a large rectangular bag.

Here's a tip for inserting the down in a bag: Put the down in a fairly large cardboard box, maybe 18" on a side or so, and tape a piece of plastic or cardboard over the top, leaving enough room to put your hands in, maybe 8" or so. With your hands in the box, put some down in a small plastic bag (I used small bread sacks), pinch the sack closed, and insert it into a compartment of the bag, open end first. then turn the bag inside out, releasing the down into the compartment. A ruler or suitable stick will help turn it inside out. You can weigh the plastic bag on a postal scale first if desired, or just estimate the quantity of down.

Using this method keeps the mess to a minimum.