All Blancpain timepieces carry a reference number which is built from three blocks. The first block identifies the specific model, with the first digit of that block indicates the model family, e.g. 5 for the Fifty Fathoms series.
The second block indicates the case material (first two, sometimes three digits) and the dial color (last two digits), e.g. 11B for a brushed steel case and 30 for a black dial.
The last block indicates the strap/bracelet and the clasp, e.g. 63B for a Barennia strap on deployant clasp or 71 for bracelet.
Here are today’s reference numbers explained in an overview. Click on the photo to enlarge (I apologize for the poor quality, but it’s better than nothing):
As you can see there are a few exceptions in each model family/first reference digit combinations.
Prior to today’s collection codes, Blancpain used different names for the model families or even only reference numbers for the categories, e.g. the Leman was previously named 2100 series and the Trilogy models were listed in the Specialties family.
I hope this short excursion into the reference number system helps you navigate through it.