I replaced a 44 gallon (I think) well bladder expansion tank because it appeared to have lost capacity, i.e. bladder leak. With the tank removed, I drained the water out of the bottom, then removed the air valve at the top and drained all the water on that side of the bladder. The tank still has a significant amount of water in it, judging by it's wieght and balance and I can hear it slousing with movement. Do these larger tanks have multiple bladders?

Not that I know of. However, if the bladder is ruptured, I would think that, when you drained the water out of the bottom, you would have gotten practically all of it since the water above the ruptured bladder would simply have drained through the rupture into the bottom of the tank and then drained out.

Are you certain the bladder is ruptured? If the top will hold pressure with the bottom drain unplugged, then the bladder would have to be OK.

I stood it upright and drained the water out the bottom. Then I tipped it so the air valve was at the lowest point, with air valve removed, and quite a bit of rusty water came out. I think it had to be ruptured in order to get any water out of the top. Definitely still water in the tank though. I suspected the multi-bladder because of the several weld seams around the tank, I assume where the bladder is located.
When I say ruptured, I mean some kind of water transfer over time. I do cycle the system from 40 to 70 psi, which is higher than normal, but the tank is supposed to be good to 150psi. I assume that to mean the bladder also.

Never heard of multiple bladders in a tank. Why would you do that? If you have a small leak in the bladder, water, under pressure would leak through. When you drain the tank, the hole would tend to collapse. Eventually the water above the bladder would be pushed out if you pressurized the tank but it could take some time. Don't think there is any doubt you have a leaking bladder.