Yes, you are correct. Upon creating invoices, only the 2019 transactions will show on your sent emails.
For future help, you can always visit our Community page for the “How Do I” steps: QuickBooks Desktop for Mac Self-help.
Resolution for 'Community page issue: 'Email history' available: Yes.
The Community page 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 Community page issue yourself by looking for a resolution described in the article. If it is a complex Community page issue or you are unable to solve the issue, you may contact us by clicking here or by using other Community page support options.
For more information about resolving issues related to Community page in Quickbooks/QBO or to get support for the issue 'Email history', click the link below: