Conditional Formatting in Excel

Below is a small sample of the data that I am working with. Each column represents a year and each row represents an account number. What I would like to do is highlight the account numbers that are unique in comparison to the prior year and that year alone. For instance for year 2 I want to know what new accounts have been created in respect to year 1 and highlight the new account numbers in year 2 (ie. account numbers 20178 and 20792). I want to do this for each subsequent year without alterating the formatting for the prior year. I am aware of conditional formatting, however, it is also highlighting for the previous year in respect to accounts that are no longer in existence. For instance in year 1 account number 83681 was deleted so the conditional formatting I am using now will also highlight 83681 and again I am only interested in highlighting new accounts. Please advise thank you greatly.

Year 1 Year 2 Year 3 Year 4
29479 29479 29479 29479
20188 20178 20178 20178
20297 20297 20297 20597
20792 20796 20796 20796
83681 00000 85251 85251