DAX query: calculating incremental growth of a value by date

Hi Hoping someone can help me out with this Dax query to create a new column of calculated values in an existing table. I'm trying to add a new column that for each row shows the incremental growth in usage over time for each unique combination of CustomerName and ProductName.

I've tried the following Dax query, but it's not properly calculating the growth.

Calc_IncGrowthOverTime = 
VAR CurrentCustName = [CustomerName]
VAR CurrentWorkLoad = [WorkloadName]
VAR EarliestDate = CALCULATE(MIN('Table1'[Date]), ALL('Table1'), 'Table1'[CustomerName] = CurrentCustName, 'Table1'[WorkloadName] = CurrentWorkLoad)
VAR SoYValue = CALCULATE(MIN('Table1'[Usage]), 'Table1'[Date] = EarliestDate, 'Table1'[CustomerName] = CurrentCustName, 'Table1'[WorkloadName] = CurrentWorkLoad)
RETURN
[Usage] - SoYValue

For rows that aren't the earliest date for that combination of CustomerName and ProductName it's caculating SoYValue as zero so isn't properly calculating the growth.

What I'd like it to return is this...

Growth = 
VAR x = CALCULATE(MIN('Table'[Date]), ALLEXCEPT('Table', 'Table'[CustomerName], 'Table'[ProductName]))
VAR y = CALCULATE(MIN('Table'[Usage]), ALLEXCEPT('Table', 'Table'[CustomerName], 'Table'[ProductName]), 'Table'[Date] = x)
RETURN 'Table'[Usage] - y