America's Castles - 1994 Prince's Palace in Monaco was released on:
USA: 1996
Because Monaco is a principality (a state ruled by princes).
Prince Ranier was a "Prince" not a king because Monaco was a Principality and not a Kingdom. Monarchs of Principality are p\Princes, and monarchs of kingdoms are Kings.
Muroge Monaco - 1982 VG was released on: USA: 1982
The Principality of Monaco - 1911 was released on: USA: 28 October 1911
Monaco - 2012 VG was released on: USA: 1 November 2012
From Monte Carlo to Monaco - 1902 was released on: USA: November 1902
Monte Carlo - Monaco 1913 was released on: USA: 1 August 1913
If you mean: how many are ruled by princes (in Europe), the answer is two: Monaco and Liechtenstein. If you mean: how many know that title as part of its recognized nobility, the answer is: all kingdoms in Europe (7) plus a number of countries where this is still a recognized rank, mostly former kingdoms such as France and Italy.
Motor Boat Race at Monaco - 1905 was released on: USA: November 1905
Over Monaco in a Hydro-Aeroplane - 1912 was released on: USA: 26 July 1912
Passport to Europe - 2004 Cote D'Azur Monaco was released on: USA: 9 May 2005
Marie - 2012 Kelly Monaco 1-6 was released on: USA: 8 October 2012