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Hey,

I couldn't resist and created sample data by myself, here you will find a pbix file. The sheet "Not yet validated" is recreating your requirement. The table "GroupOfStates" represents your data that you use in your post. I also created a table "Sequence", this table represents the sequence of categorical Events (meaning a column that is not represented by a numerical or date data type).

This measure in the table "GroupOfStates" calculates the Previous Value:

PreviousStateValue = 
SUMX('GroupOfStates'
    ,var currentGroup ='GroupOfStates'[Group]
    var currentState = 'GroupOfStates'[State]
    var previousState = 
    CALCULATE(FIRSTNONBLANK('Sequence'[Predecessor],1)
        ,'Sequence'[State] = currentState
    )
    return
    CALCULATE(
        SUM('GroupOfStates'[Amount])
        ,FILTER(ALL('GroupOfStates')
            ,'GroupOfStates'[Group] = currentGroup && 'GroupOfStates'[State] = previousState
        )
    )
)

This screenshot looks quite similar to your requirement:

Hopefully this is what you are looking for.

Regards

Tom