On Tuesday and Wednesday, the government sent information to insurers listing everyone who had enrolled in a health plan through the federal marketplace. Insurers are supposed to compare the information with their own records and with the daily reports they received from the government over the last 10 weeks.

Insurers said they had found many discrepancies and errors and that the government was overstating the improvements in HealthCare.gov.

In some cases, they said, the federal government reported that the home address for a new policyholder was outside an insurer’s service area. In other cases, a child was listed as the main subscriber — the person responsible for paying premiums — and parents were listed as dependents.

In some cases, children were enrolled in a policy by the federal government and parents were left off, or vice versa. In other cases, the government botched up the members of a family: A child or spouse was listed two or three times in the same application in late November. Such errors can have financial implications, increasing the amount of premiums that a family is required to pay.