Compare your clarinet's serial number to the list of Buffet Crampon serial numbers at Clarinetperfection.com to ascertain the year of manufacture. Clarinetperfection.com also has a page dedicated to identifying Buffet Crampon models that can help you learn more about your clarinet.
Buffet Crampon has been making clarinets since 1836, although serial number records are only available from 1885 onwards. Until the end of 1927, serial numbers were a mixture of letters and numbers; since then, however, Buffet Crampon has numbered its clarinets in the order that they are made. Clarinet number one was produced in 1928, and the most recent serial number on Clarinetperfection.com is 545021, manufactured in 2005. According to Clarinetperfection.com, clarinets manufactured between 1965 and 1979 are some of the most desirable; their serial numbers lie in the 83000 to 200000 range.
While a serial number can tell you the year the clarinet was made, you also need to know the model if you are interested in how much it is worth. Clarinetperfection.com has images and explanations of key features for models dating from 2012 back to the late 19th century that will help you identify the type of clarinet along with the year of manufacture. You can find vintage Buffet Crampon clarinets for sale on eBay.