No answer to your question. I looked carefully at pictures 463 and 469 and I see lighter shade on wood and brass in 469 and darker shade on wood and brass in 463.
Is that shading I am seeing what you are asking about?
Are you wanting to equalize the look on the wood, the brass, or both?
You suggest the Browning process may have caused this, speculation?
The shading is quite distinguishable, does it only exist at the one location?
Could it be caused by light it has been exposed to while on display?
It is very interesting