Except the loss of the nose was documented long before Napoleon...and in fact, said documentation is pretty specific. From Wikipedia:
"The Egyptian Arab historian al-Maqrīzī, writing in the 15th century AD, attributes the loss of the nose to iconoclasm by Muhammad Sa'im al-Dahr, a Sufi Muslim from the khanqah of Sa'id al-Su'ada. In AD 1378, upon finding the Egyptian peasants making offerings to the Sphinx in the hope of increasing their harvest, Sa'im al-Dahr was so outraged that he destroyed the nose, and was hanged for vandalism. Al-Maqrīzī describes the Sphinx as the "talisman of the Nile" on which the locals believed the flood cycle depended.
A story claims that the nose was broken off by a cannonball fired by Napoleon's soldiers and that legend still lives on today. Other variants indict British troops, the Mamluks, and others. However, sketches of the Sphinx by the Dane Frederic Louis Norden, made in 1737 and published in 1755, illustrate the Sphinx already without a nose."