I created a journey and then later associated a DataTable with that journey.
I noticed the columns names used in that DataTable did not appear in the journey parameters and I needed to manually add.
This can be a little frustrating if you have many columns.
If on creation time of the journey you associated a DataTable with that journey then the journey parameters appeared.
In my case, I did the journey first and then decided to add a DataTable later.
When editing a test, you can now use all variables available in associated datatables regardless of when a datatable was associated with the test.