Each face has a different serial number (I have 5 pieces remaining from the original find of 10): 32/200; 92/207; 87/99; 124/193; 38/138. Not a common practice from what all I've seen.

Not being able to locate the other serial numbers of the pieces I sold, is there a pattern/arrangement of numbers from what's listed above?

The pieces are probably early-1900's according to the monogram (Casino Municipal-Nice)... and are a ceramic-type material; very similar to a CHIPCO full-graphic.