First - In 2019 do Client > Update database. That may make them appear. If not:

Go back to 2018 and start the proforma again for any client. In the 3rd step you will see Client data destination directory. Note that and exit. Now go to 2019 and press F10 and in the 1st tab, look down the list to find Data path. Make sure those two paths are the same. If not,  repeat the proforma. Also go to the path you did the transfer to and delete that data to save drive space.