Date table with no date column

Here is one way to do it with your example table structure.  It involves unpivoting your data, splitting the column with the year info and creating a new Date column.  To see how it works, just create a blank query, go to Advanced Editor, and replace the text there with the M code below.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCkgtysxPUdJRCk7MSS1WMDJEMA3gTENLpVidaCWvxDygkCkQm4FpkJhbahKQbQIVNwGL+SYWQfmmcHWOBUVQdWZgDFFXiaHOqzQPScwEKpaDpBci5liajmQvRG9wagGSXqAdsQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Period = _t, #"(blank)" = _t, #"(blank).1" = _t, #"(blank).2" = _t]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Period", type text}, {"Sales 21", Int64.Type}, {"Sales 20", Int64.Type}, {"Sales 19", Int64.Type}}),
    #"Unpivoted Other Columns" = Table.UnpivotOtherColumns(#"Changed Type", {"Period"}, "Attribute", "Value"),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Unpivoted Other Columns", "Attribute", Splitter.SplitTextByEachDelimiter({" "}, QuoteStyle.Csv, false), {"Attribute.1", "Attribute.2"}),
    #"Removed Columns" = Table.RemoveColumns(#"Split Column by Delimiter",{"Attribute.1"}),
    #"Renamed Columns" = Table.RenameColumns(#"Removed Columns",{{"Attribute.2", "Year"}, {"Value", "Sales"}}),
    #"Added Custom" = Table.AddColumn(#"Renamed Columns", "Date", each Date.FromText("20"&[Year]&"-"&[Period]&"-1")),
    #"Removed Columns1" = Table.RemoveColumns(#"Added Custom",{"Year"})
in
    #"Removed Columns1"

Pat