Comparison Date (Year on Year)

Hi JPAnalytics 

Not sure I've understood completely, but give this a  go:

let
  Source = List.Dates(#date(2018, 1, 1), 100000, #duration(1, 0, 0, 0)),
  #"Converted to Table" = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
  #"Changed Type" = Table.TransformColumnTypes(#"Converted to Table", {{"Column1", type date}}),
  #"Renamed Columns" = Table.RenameColumns(#"Changed Type", {{"Column1", "Date"}}),
  #"Filtered Rows" = Table.SelectRows(#"Renamed Columns", each [Date] <= Date.EndOfYear(Date.From(DateTimeZone.RemoveZone(DateTimeZone.SwitchZone(DateTimeZone.FixedUtcNow(), +10))))),
  #"Week Day" = Table.AddColumn(#"Filtered Rows", "Week Day", each Date.DayOfWeekName([Date])),
  #"Week Day Short" = Table.AddColumn(#"Week Day", "Week Day Short", each Text.Start([Week Day], 3)),
  #"Week Day No." = Table.AddColumn(#"Week Day Short", "Week Day No.", each Date.DayOfWeek([Date],Day.Monday)+1),
  Week = Table.AddColumn(#"Week Day No.", "Week", each Date.WeekOfYear([Date], Day.Sunday)),
  #"Week (ISO)" = Table.AddColumn(Week, "Week (ISO)", each if Number.RoundDown((Date.DayOfYear([Date])-(Date.DayOfWeek([Date], Day.Monday)+1)+10)/7)=0 then Number.RoundDown((Date.DayOfYear(#date(Date.Year([Date])-1,12,31))-(Date.DayOfWeek(#date(Date.Year([Date])-1,12,31), Day.Monday)+1)+10)/7) else if (Number.RoundDown((Date.DayOfYear([Date])-(Date.DayOfWeek([Date], Day.Monday)+1)+10)/7)=53 and (Date.DayOfWeek(#date(Date.Year([Date]),12,31), Day.Monday)+1<4)) then 1 else Number.RoundDown((Date.DayOfYear([Date])-(Date.DayOfWeek([Date], Day.Monday)+1)+10)/7)),
  #"Changed Type1" = Table.TransformColumnTypes(#"Week (ISO)",{{"Date", type date}, {"Week Day", type text}, {"Week Day Short", type text}, {"Week Day No.", Int64.Type}, {"Week", Int64.Type}, {"Week (ISO)", Int64.Type}}),
  #"Added Custom" = Table.AddColumn(#"Changed Type1", "Comparison date", each List.Max(Table.SelectRows(#"Changed Type1", (inner) => [#"Week (ISO)"] = inner[#"Week (ISO)"] and [#"Week Day No."] = inner[#"Week Day No."])[Date]), type date)
in
    #"Added Custom"