Calculate[calling-measure] vs Calculate(writing-measure)

[Lhans]

Hello everyone, I'd be very greatful if someone could help me out!

I am trying to compute new customers [newcustomercount] and have used the dax code used here for this:
https://www.sqlbi.com/articles/computing-new-customers-in-dax/

I have also created a copy of my 'Date' table called 'PreviousDate'  to be able to select a single month in a visual and get 6 months filter the previous 6 months of the date table. Code for this has come from here:
https://www.youtube.com/watch?v=d8Rm7dwM6gc&t=601s

Here is a link to my pbix file in case you'd like to check it out! Thanks if you do!
https://drive.google.com/drive/folders/1j93uX4dUL6JoTJxDt3LMPWdHQD0_Nssj?usp=sharing

The Problem

I have noticed that I get a different result when,

calling a measure within calculate:

[prev6mths|callingmeasure]

.........
VAR Result =
    CALCULATE(
        [newcustomercount],
        REMOVEFILTERS ('Date'),............

vs.

writing the measure within calculate:
[prev6mths|writtingmeasure]
................

VAR Result =

    CALCULATE(

        COUNTROWS (

        FILTER (

            CALCULATETABLE (

                ADDCOLUMNS (

                    ...............

Results:

Relationships:

My Measures:

newcustomercount =

COUNTROWS (

    FILTER (

        CALCULATETABLE (

            ADDCOLUMNS (

                VALUES ( NewRevenue[Account_Id] ),

                "DateOfFirstBuy", CALCULATE ( MIN ( NewRevenue[Report_Month] ) )

            ),

            ALL ( 'Date' )

        ),

        CONTAINS ( VALUES ( 'Date'[Date] ), 'Date'[Date], [DateOfFirstBuy] )

    )

)

prev6mths|callingmeasure =

VAR NumOfMonths = -6

VAR ReferenceDate =

    MAX ( 'Date'[Date] )

VAR PreviousDates =

    DATESINPERIOD ( 'PreviousDate'[Date], ReferenceDate, NumOfMonths, MONTH )

VAR Result =

    CALCULATE (

        [newcustomercount],

        REMOVEFILTERS ( 'Date' ),

        KEEPFILTERS ( PreviousDates ),

        USERELATIONSHIP ( 'Date'[Date], 'PreviousDate'[Date] )

    )

RETURN

    Result

prev6mths|writtingmeasure =

VAR NumOfMonths = -6

VAR ReferenceDate =

    MAX ( 'Date'[Date] )

VAR PreviousDates =

    DATESINPERIOD ( 'PreviousDate'[Date], ReferenceDate, NumOfMonths, MONTH )

VAR Result =

    CALCULATE (

        COUNTROWS (

            FILTER (

                CALCULATETABLE (

                    ADDCOLUMNS (

                        VALUES ( NewRevenue[Account_Id] ),

                        "DateOfFirstBuy", CALCULATE ( MIN ( NewRevenue[Report_Month] ) )

                    ),

                    ALL ( 'Date' )

                ),

                CONTAINS ( VALUES ( 'Date'[Date] ), 'Date'[Date], [DateOfFirstBuy] )

            )

        ),

        REMOVEFILTERS ( 'Date' ),

        KEEPFILTERS ( PreviousDates ),

        USERELATIONSHIP ( 'Date'[Date], 'PreviousDate'[Date] )

    )

RETURN

    Result

Thanks for reading, I would be very greatful if anyone could help me out!