= Table.NestedJoin

It sounds like all your want to do is take the max week for each Order and then call it a closed service order on the max week.  

Just Group By Order, Operation Max Week, Operation All Rows.  Expand and add custom column Week = Max Week.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTSUTJUitWJVnKCs0BiRnAxI7iYMVwMwTIBs5yBLFM4y0wpNhYA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Order = _t, Week = _t]),
    #"Grouped Rows" = Table.Group(Source, {"Order"}, {{"Max Week", each List.Max([Week]), type nullable text}, {"Rows", each _, type table [Order=nullable text, Week=nullable text]}}),
    #"Removed Columns" = Table.RemoveColumns(#"Grouped Rows",{"Order"}),
    #"Expanded Rows" = Table.ExpandTableColumn(#"Removed Columns", "Rows", {"Order", "Week"}, {"Order", "Week"}),
    #"Added Custom" = Table.AddColumn(#"Expanded Rows", "Closed", each [Week] = [Max Week])
in
    #"Added Custom"

Copy and paste entire code into blank query to see a full example.