IThis year, I upgraded my 2015 QB for MAC to 2019 version. When I open the 2019 version, my data for 2016 & 2017 is missing! Can anyone help me fix that?

Usually this means the file you upgraded isn't your most recent copy.  Search with spotlight for .qb2016 and see what files show up.  Look for the largest one and open that with 2019.

The other possibility is data damage and running File->Utiltiies->Rebuild in QuickBooks should fix it. But that's much less likely.

I do not have a 2016 version. All my data is in the 2015 version of QB (For 2016 & 2017, and earlier). When I open my 2019 version, it only shows my data to the end of 2015. How do I move the rest of the data (For 2016 & 2017) over to the 2019 version?

One more attempt to communicate my issue: When I open the 2019 QB file for my company, it only shows my data up to end of 2015. The earlier version I was using (2015) contains all my 2016 & 2017 transactions. How can I get the missing data transferred from 2015 version to 2019?

Glad to see you again, @ter88meh.

I can provide some clarifications about restoring a company file into the latest version in QuickBooks Desktop.

If you've created a recent backup copy of the company file prior to the upgrade that you made, all of your data should be restored completely on the latest version of QuickBooks.  

To single this issue out, you can try running the verify and rebuild process, as mentioned by IntuitBrooks above. Verifying the data self-identifies data issues within a company file while rebuilding the data resolves data integrity issues.

To do that:

1. Click on File at the top menu bar.
2. Select on Utilities.
3. Click on Rebuild Data.
4. Select OK when you see Rebuild has completed.

Once done, you can proceed with verifying the data:

1. Click on File.
2. Select on Utilities.
3. Click on Verify Data.

For detailed instructions on these steps, please refer to this article: Resolve data damage on your company file.

Also, here's a link that you can check out about finding hidden files and folders in QuickBooks Desktop for your future reference.

If the problem continues, I'd recommend getting in touch with our Customer Care Team. They have extra tools like screen-sharing that can help verify what's causing the issue.

I'm just a reply away if you need additional assistance with this concern. I'd be pleased to help you out. Have a nice day ahead.

Sorry - I meant to say search for .qb2015 with Spotlight to find all copies of your QuickBooks Mac 2015 version.  Then open the largest one in QB Mac 2019.