What constitutes the differences, if any, between the typical charges by battle cavalry in the years between 1758 and 1815 and 'massed cavalry charges?' Certainly 'reserve corps of cavalry' wasn't all that new--There were Allied cavalry corps at Austerlitz in 1805. Certainly large units of cavalry attacking together weren't new on the scene--there are a number of Allied examples from the Revolutionary wars and after, why before the Allied spat of reforms.
When Murat organizes 10,000 cavalry at Eylau for an assault, I am sure that counts, but charges with those numbers was a fairly rare event, and not all that successful, IIRC.
Regardless of whatever constitutes the French 'massed cavalry charges', was their existance and any unique power they might of had more the ability of the French to maneuver large numbers of horsemen, rather than having particularly unique organizations or large numbers?