Create new column to check the duplication with certain condition

This REQUIRES that the data is sorted exactly how it is shown in your example.  It also assumes Accrual always sorts before Actual as well.  That should be the case if it is in alphabetical order.  All this does it shift the table up one row and compares the current row values to the next row's values.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("nZI9C8IwEIb/imTuYNIPXfPVZnKodJDSQUo3qaCtv98DbYp4kEuX90Lg4Tm4t22Z5CJVWV6whNXDaxjnYX3tZD/N1xt8SCkhbVND8j3EhXUJFVZKeTglw/3jQ2utIZuzgcyiaWOMp/PYxa21G+BFXZalp7kojpHyqqo24YveObee7JAKGKcIPYL/6fX9OX1HTFVQLFySX4xeD5wLFwNdM1wJXEcpAyqk1ABXUgqAKvHTd28=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t, #"Data Group" = _t, #"Data Type" = _t, #"Data Code" = _t, Currency = _t, Amount = _t, Checking = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", type text}, {"Data Group", type text}, {"Data Type", type text}, {"Data Code", type text}, {"Currency", type text}, {"Amount", Int64.Type}, {"Checking", type text}}),
    prior_step = Table.RemoveColumns(#"Changed Type",{"Checking"}),
    tbl = Table.SelectColumns(prior_step, {"ID","Data Group","Data Type", "Data Code"}),
    temp_columns = Table.FromColumns(
        Table.ToColumns(prior_step) & Table.ToColumns(Table.RemoveFirstN(tbl,1)),
        Table.ColumnNames(prior_step) & Table.ColumnNames(Table.PrefixColumns(tbl,"temp"))
        ),
    check_column = Table.AddColumn(temp_columns, "Check", each if [Data Code] <> [temp.Data Code] then "Y" else if [ID] = [temp.ID] and [Data Group] = [temp.Data Group] then "N" else "Y"),
    remove_temp_columns = Table.RemoveColumns(check_column, {"temp.ID","temp.Data Group","temp.Data Type","temp.Data Code"}) 
in
    remove_temp_columns