What do the codes mean in Box 16 of the K-1 for S Corporations?

Items affecting shareholder basis
A: Tax-exempt interest income
B: Other tax-exempt income
C: Nondeductible expenses
D: Distributions
E: Repayment of loans from shareholders
F: Foreign taxes paid or accrued

See the Schedule K-1 (Form 1120-S) instructions  for more info about these codes.

What if the boxes on my K-1 don't match?