1095-A First 4 months of Column B and C show zero

Did they not make the premium payments until May? Did they sign in to the Marketplace and list a life change of some sort? Someone moved from Family plan to personal, or employer to marketplace? Did you read the 1095-A instructions? Examples:

Part III—Coverage Information
Enter information in Part III, lines 21 through 32, for each month of coverage. This information is determined on a monthly basis and may change during the year if there is a change in enrollment or other circumstances that affect eligibility for, or the amount of, the premium tax credit.

In some cases, the information provided at enrollment may not indicate which covered individuals are members of the recipient's family and are not eligible for other health coverage. (Such information may not be provided, for example, because no financial assistance was requested.)

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If a policy is terminated by an issuer for nonpayment of premiums and advance credit payments are made, enter -0- for a month in which the covered individuals have coverage but the premiums are not paid (generally, the first month of a grace period)