Well, after my best estimate of the Erard Piano's age based upon serial numbers (I guessed 1859) it turns out that an artisan's mark on whippen #11 "A. Royer"--I have seen that name before in photos of other Erards from the period--indicates a manufacture date of 1858. 
These other photos show the installation of the new back rail felt (the green felt ribbon) and the regulation of the key height...
