Steps:

1. Either with code or manually, cell A2 and below will move down a cell
2. New value will be entered into blank A2
3. Either with code or manually, cell B2 and below will move down a cell
4. New value will be entered into blank B2
5. Steps 1 to 4 will be repeated maybe 20 to 30 times each day.

Rules:
1. No value will be added into Column B that doesn't exist in Column A.
2. Column A will always contain values that haven't been entered into Column
B.