Who plays bass on Old Brown Shoe?
In an interview George says it was him, doing his thing.
On the demo where he does indeed play bass it sounds the same, especially the bridge part that was always outstanding.
One reference I have says Paul doubles George's guitar on bass.
All the rest say it's Paul (or don't indicate at all).
We have many of the same books and reference tools but some of us have better than others. Tho I have most of the usual ones, I'm sure someone (Maria?) here can say with a tad more certainty than what I've indicated above.
After hearing George's demo I personally think it was indeed him. Yes, Paul played the jangly piano on the initial take, but could have overdubbed the bass the second time around.