Finally I was able to get more info about this dagger. This dagger is constructed of 1660 blade and 19th century mounts. That explains the variance in quality in the mounts vs. the blade. Several antique arms dealers confirmed that.
The makers mark belongs to French blacksmith family and used in 17th and 18th century. Similar markers mark with the bunch of grapes, the CO letters, teardrop shaped cartouche and beaded border appears on a French dress sword ca. 1700 in the Metropolitan Museum of Art collection, and can be found in the Bashford Dean catalogue (no. 17, plate XII, page 123), see picture below. The catalog can be downloaded here:
MET Catalogue This dagger�s blade is earlier than 1700, i.e. same family, different smith, made around 1650-1660. It�s impossible to tell who exactly produced the hilt and the scabbard, but because mounts are cast rather than chiseled the assumption was made that it was done in 19th century.
Still a beautiful dagger and I really like it. I'm adding better pictures, so you can see all the details and appreciate the amount of work that was put into it.