Both Stanhope and Wellington can be regarded as reliable reporters though the precision of a quote made over 20 years later can be doubted, but the original remark was based on conversation overheard by the spy, which is another matter.

As for the mobile brothel, whatever the exact phrasing, it appears to have been a fair description, to judge by Napoleon's reaction:

To general Clarke, Duc de Feltre Minister of War Mayence 31st July 1813

Give orders that all wives of generals, officers and government employees, and all women of bad character, including those dressed as men, who have come from Spain, and are now at Bayonne, and in the Departments of the Landes and the Basse Pyrenees, are instantly to be sent back across the Garonne, and that forty-eight hours after the issue of the order you will cause the officer commanding the division to publish on this subject, all those who have not obeyed are to be arrested by the civil and military authorities and taken to their homes. The loose women will be confined in the Saltpetriere. You will take care that the wives of the three generals, G-----, F------ and V-------, are not only sent back across the Garonne, but straight to their own homes.

regards,

Susan