Personally I would go with the 3 month old backup and work forward.  But before I was done, I would probably sign up with Carbonite so this doesn’t happen again.

Resolution for 'Carbonite issue: 'computer crashed. have a flash drive back up 3 months old.' available: Yes.

The Carbonite issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Carbonite issue yourself by looking for a resolution described in the article. If it is a complex Carbonite issue or you are unable to solve the issue, you may contact us by clicking here or by using other Carbonite support options.

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