The Centigraphe F is a "boutique piece" only in that it is made-to-order, so it can only be bought via an official boutique - no different than say, the Sonnerie Souveraine. There has been no deception from F.P. Journe on this; when F.P. Journe makes a limited edition, the serial number is inscribed as such (e.g., X/5, XX/28, XX/99, etc.).
In any case, very few Centigraphe F were ever made - so if you have one, rest assured you are in very select company.