Calculated Column that evaluates multiple rows

Hi, ShocKrates 

Thanks for gmsamborn's concern about this issue.

I am glad to help you.

You can refer to my DAX to New Column:

First Spend Month = 
CALCULATE(
    MIN('Table1'[Spend Date]),
    ALLEXCEPT('Table1', 'Table1'[Project ID])
)

Or

First Spend Month = 
VAR CurrentProjectID = 'Table1'[Project ID]
RETURN
CALCULATE(
    MIN('Table1'[Spend Date]),
    FILTER(
        'Table1',
        'Table1'[Project ID] = CurrentProjectID
    )
)

This is test result:

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Fen Ling,
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