It calls for the inside board to be 38″. But it cant go up 38″ on the inside because of the top cross members. Second, If you are going to back the front of the bar with ply wood then put the vaneer, that wont jive with the side panels if you are backing it from the inside.
Both sheets are applied to the OUTSIDE of the framing.
There is a outside layer of an INNER and OUTER sheet.
The inner sheet is OSB, to give it strength, the outer sheet is the plywood or bead board of your choice.
Yes, that may sound confusiing, but it you look at the drawings, you should get the idea.
The inside of the bar is bare for whatever you want to place there.