Sometimes IDing the country of origin of your Black Widow can be a little confusing.  After looking through countless pics and auctions I've come to the conclusion that the simplest way to tell if it's made by Mosrite is to see if it has 4 neck screws with the wavy neckplate as shown below.

Mosrite-made Black Widow neckplate

The distinction between Bartell instruments and Japanese instruments may be a little more difficult.  Both used a 3-bolt neck mount with the 3rd bolt on the front of the guitar but it would seem the Bartell guitars had only 22 frets where the Japanese and Mosrite versions had 24.  Also, the Bartell headstock should be longer with more space above the D and G strings although there has been at least one guitar seen with a short headstock.

Serial numbers for Japanese guitars and basses tended to be either 4 digit numbers or the letters 'BA" followed by a 4 digit number.  Mosrite versions started with "BC" for the guitars and "BD" for the basses, both followed by a 4 digit number.