two different Dates count in one dashboard

Have a single calendar table with each date a unique value.

Create two relationships between your fact table and your calendar table:

1. Calendar[Date] ---> Fact[Arrival Date] (one to many)
2. Calendar[Date] ---> Fact[Decomissioning Date] (one to many) Inactive

Then you can have two measure to display on the same chart:

Rows (Arrival) = COUNTROWS('Fact Table Name')

And

Rows (Decommission) = Calculate(COUNTROWS('Fact Table Name'), USERELATIONSHIP('Calendar'[Date],'Fact Table Name'[Decommission Date]))

This should do it- you switch the relationship within the DAX measure, without a duplicate calendar table.

Note that this is a stacked area chart. This is the expected behavior.

Either:

1. Change into a (non-stacked) area chart 

or 2. Switch the order of the measures in the visualization pane: