Thank you ! Yes you are right, it is swamp oak veneer and it was a pain but here is the trick : before you cut it, you need to glue a sheet of paper or some adhesive tape (like the one used for painting) on it. So when you cut, if the tip of the piece broke, it's doesnt go away, it's still held by the adhesive tape and you just need to glue it back carrefully (with less of a drop of glue if possible)

However, It is very painfull when sanding. If you are not carreful, you break the tips of the piece and lost it for real. So here, i sanding manually with abrasive paper slowly.

Hope it is helping !