How to Accumulate Values by Date and Customer, Resetting When the Assigned Person Changes?

Hi robertobrsp, check this:

Output

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMtE3MFTSUXIEYl/HIE8QbWigFKsDkzQGCjghSRohS5pCJR19XPxBcqZKsbEA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [DATE = _t, CUSTOMER = _t, PERSON = _t, VALUES = _t]),
    ChangedType = Table.TransformColumnTypes(Source,{{"VALUES", type number}}),
    Helper = [ dates = List.Transform(ChangedType[DATE], (x)=> Date.FromText(x & "/01", [Format="yyyy/MM/dd"])),
    minDate = List.Min(dates),
    maxDate = List.Max(dates),
    headers = Table.FromList(List.Generate( ()=> minDate, each _ <= maxDate, each Date.AddMonths(_, 1), each Date.ToText(_, [Format="yyyy/MM", Culture="en-US"])))
  ],
    StepBack = ChangedType,
    GroupedRows = Table.Group(StepBack, {"CUSTOMER"}, {{"All", each
      [
        // _Detail = GroupedRows{0}[All],
        _Detail = _,
        _ShiftedValues = Table.FromColumns(Table.ToColumns(_Detail) & {{null} & List.RemoveLastN(_Detail[VALUES])}, Value.Type(Table.FirstN(_Detail, 0) & #table(type table[Prev VALUES = number], {}))),
        _Ad_NewValue = Table.AddColumn(_ShiftedValues, "NewValue", each [VALUES] + ([Prev VALUES] ?? 0), type number),
        _Ad_Index = Table.AddIndexColumn(_Ad_NewValue, "Index", 0, 1, Int64.Type),
        _MergedQueries = Table.NestedJoin(_Ad_Index, {"DATE"}, Helper[headers], {"Column1"}, "_Sorted", JoinKind.FullOuter),
        _Expanded = Table.ExpandTableColumn(_MergedQueries, "_Sorted", {"Column1"}, {"Column1"}),
        _Sorted = Table.Sort(_Expanded,{{"Column1", Order.Ascending}}),
        _FilledDown = Table.FillDown(_Sorted, Table.ColumnNames(_Sorted)),
        _RemovedColumns = Table.RemoveColumns(_FilledDown,{"DATE", "VALUES", "Prev VALUES"}),
        _Pivoted = Table.Pivot(_RemovedColumns, List.Distinct(_RemovedColumns[Column1]), "Column1", "NewValue"),
        _Filtered = Table.SelectRows(_Pivoted, each [CUSTOMER] <> null),
        _Sorted2 = Table.Sort(_Filtered,{{"Index", Order.Ascending}}),
        _RemovedColumns2 = Table.RemoveColumns(_Sorted2,{"Index"})
      ][_RemovedColumns2], type table}}),
    Combined = Table.Combine(GroupedRows[All])
in
    Combined