Find mismatches

I have tried 3 times to post followup questions but I keep getting this: "Content Not Permitted, two-four-seven is not allowed in the community. Remove it and try again." (Except it uses the numerals, not the spelled-out numbers.)  I don't know what it is that's triggering this denial, so I will describe what I want to do.  I have Column A, ID numbers, Column B, the same type of ID numbers, and Column C, data that goes with the Column B ID numbers.  The whole universe of ID numbers is in Column A.  Most of those facilities have data for Column C, but some do not.  I want to be able to spot the mismatches between Column A and B, and insert blank cell(s) in Column B and C such that Column A and B match.  When I do that, I want the entire rest of Column B to automatically adjust to meet the rule, in which mismatches are highlighted by color fill.  Does that make sense?