Cut-off Date from Different Table

Hi RobRayborn  - Create a calculated column or measure to identify the first order date per product.

eg: 

FirstOrderDate =
CALCULATE(
MIN('Orders Taken'[DATE CREATED]),
ALLEXCEPT('Orders Taken', 'Orders Taken'[Product])
)

Now write the Forecast Measure that blanks quantities after the first order

Adjusted Forecast Quantity =
VAR CurrentProduct = SELECTEDVALUE('Product'[Product])
VAR CurrentShipDate = SELECTEDVALUE('Date'[Date])

VAR FirstOrderDateForProduct =
CALCULATE(
MIN('Orders Taken'[DATE CREATED]),
FILTER('Orders Taken', 'Orders Taken'[Product] = CurrentProduct)
)

RETURN
IF(
NOT ISBLANK(FirstOrderDateForProduct) && CurrentShipDate >= FirstOrderDateForProduct,
BLANK(),
SUM('Forecast'[Quantity])
)

Place this Adjusted Forecast Quantity measure on visuals using the Date, Product, and Forecast context.

It will show the original forecast only before any order activity started per product. Hope this works.