It is nice to have photo's for reference. These show the condition of the woodwork prior to beginning the work
This line in the lid is underneath the mahogany veneer. It is always interesting how this shows through the wood. It may be material used to seam the underlayer cross banding used in constructing a stable panel for use in the lid.

This may show through the new finish.
This is an example of loose veneer on the piano. This must be replaced or it will fail under the new finish. usually in the form of a new finish that cracks along the edges. Expansion and contraction of the case loostens may of these types of edges.