Let me share two scenarios and help make sure you're able to migrate all your files in QuickBooks Desktop 2019.
The possible reason why all recent invoices didn't merge is that you may have restored an older or outdated company file. It's recommended to restore the latest backup copy file in the newer version of QuickBooks.
If you're trying to restore a file from the backup and data is missing, you'll have to make sure that the backup file is updated. Here's how to create a backup file:
Once done, you can now restore your backup file to QuickBooks 2019. For your reference, feel free to read this article: Restore a Backup (.dmg)
But if the data if missing after the upgrade of your company file, let's find the most current backup. Here's how:
In the Search programs and files dialog box, search for *.qbb or *.qb.
When the search completes, make note of the file's location, size, and the date modified.
With QuickBooks closed, double-click on the File Name or Icon of the file that has the most recent timestamp and is the largest.
To ensure that you've selected the correct file, run a Custom Transaction Detail report for all dates to view the latest transaction entered. Just go to Report, select Custom Report, and choose Transaction Detail.
Once done, you can now upgrade the company file to QuickBooks 2019. For your reference, you can check out this article for the detailed steps and information: Convert your File.
In case you need tips and related articles in the future, visit our QuickBooks Community help website for reference: QBDT for Mac Self-help.
Please know that you can always get back to this post if have any other concerns. I'll be right here to help.