The score in the "B" column is the baseline score. It is the number of questions the student answers correctly the first time the student is tested (no matter on what date or during which marking period that happens). The only way for this B score to change is if you delete the baseline test.
The scores in the numbered columns are the current number of correct answers for that marking period. The "1 column" referred to below is the score for the 1st marking period.
Please see below for how it is possible for the B column and 1 (or other) column(s) to have varying scores:
If the B score is 0, but the 1 column has a number, then the following occurred: The first time the test was given, any (or all) questions were marked incorrect. This will happen even if just one question was marked incorrect and the test was closed. Then at some point during the 1st marking period, the student was tested again and got at least one question correct.
If the B score is the same as the 1 column, then one of the following occurred: 1. The test was only given once. 2. The test was given more than once, but the student did not get any additional answers correct.
If the B score is smaller than the 1 column (most common), then the following occurred: The test was given more than once, and the student answered more questions correctly on the 2nd (or 3rd, etc) time the test was given.
If the B score is larger than the 1 column, then one of the following occurred: 1. The test was given and the baseline score recorded. Then when given a 2nd time, Retest All was selected, and the student did not answer as many correctly as the first time. 2. The test was given later than the 1st marking period (let's say the 2nd marking period). The B score is the first score tested, the 1 column will remain 0, and the 2 column will continue to work with the rules stated above.