combining Excel files with dfferent columns

Hello - another option would be to normalize the tables without a mapping table prior appending.  This solution dynamically removes the years from the column names and places it in two normalized columns: Actuals Year and Forecast Year.  I have included explanations for each step in the query script below.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcgQCJR0lQyNjEyCFjAJyEvNAMgZAAKURFJIkjIqNBQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Project Title" = _t, #"Project Number" = _t, Column1 = _t, Column2 = _t, Column3 = _t, Column4 = _t, #"2022 PLAN" = _t, #"2022 Budget" = _t, #"Jan Actual Spend (2022)" = _t, #"Feb Actual Spend (2022)" = _t, #"2023 PLAN" = _t, #"Jan Forecast Spend (2023)" = _t, #"Feb Forecast Spend (2023)" = _t]),
    // --------------------------------------------------------
    // Store some variables 
    // --------------------------------------------------------
    // The column names actually appearing in the source file.
    FileColumnNames = Table.ColumnNames ( Source ),
    // The year appearing in the Actual Spend columns.
    GetYear_Actual = Text.Select (
        List.First (
            List.Select (
                FileColumnNames, each Text.Contains ( _, "Actual Spend", Comparer.OrdinalIgnoreCase ) 
            ) 
        ), {"0".."9"}
    ),
    // The year appearing in the Forecast Spend columns.
    GetYear_Forecast = Text.Select (
        List.First (
            List.Select (
                FileColumnNames, each Text.Contains ( _, "Forecast Spend", Comparer.OrdinalIgnoreCase ) 
            ) 
        ), {"0".."9"}
    ),
    // Get a list of column names including the word 'Plan' (case non-sensitive), excluding the first.
    DuplicatePlanColumns = List.RemoveFirstN ( 
        List.Select ( 
            FileColumnNames, each Text.Contains ( _, "Plan", Comparer.OrdinalIgnoreCase ) 
        )
    ),
    // Get a list of column names that start with 'Column' (case non-sensitive).
    GenericColumnNames = List.Select ( 
        FileColumnNames, each Text.StartsWith ( _, "Column", Comparer.OrdinalIgnoreCase ) 
    ),
    // Combine duplicate plan columns and generic columns into one list.
    ColumnNamesToRemove = List.Combine ( { DuplicatePlanColumns, GenericColumnNames } ),
    // --------------------------------------------------------
    // Clean up the column names. 
    // --------------------------------------------------------
    // Remove specific columns from the source table.
    RemoveColumns = Table.RemoveColumns ( Source, ColumnNamesToRemove ),
    // Remove numbers (years), parenthesis and leading/trailing spaces.
    TransformedFileColumnNames = Table.TransformColumnNames (
        RemoveColumns,
        each Text.Trim ( Text.Remove ( _, {"0".."9", "(", ")"} ) )
    ),
    // --------------------------------------------------------
    // If they don't already exist, add years columns to the table. 
    // --------------------------------------------------------
    AddYear_Actual = 
        if not Table.HasColumns ( TransformedFileColumnNames, {"Actual Spend"} ) 
        then Table.AddColumn ( TransformedFileColumnNames, "Actual Year", each GetYear_Actual, Int64.Type )
        else TransformedFileColumnNames,
    AddYear_Forecast = 
        if not Table.HasColumns ( AddYear_Actual, {"Forecast Spend"} ) 
        then Table.AddColumn ( AddYear_Actual, "Forecast Year", each GetYear_Forecast, Int64.Type )
        else AddYear_Actual
in
    AddYear_Forecast

You can put it in a function like this:

let
    fn = ( Table as table ) =>
let
    Source = Table,
    // --------------------------------------------------------
    // Store some variables 
    // --------------------------------------------------------
    // The column names actually appearing in the source file.
    FileColumnNames = Table.ColumnNames ( Source ),
    // The year appearing in the Actual Spend columns.
    GetYear_Actual = Text.Select (
        List.First (
            List.Select (
                FileColumnNames, each Text.Contains ( _, "Actual Spend", Comparer.OrdinalIgnoreCase ) 
            ) 
        ), {"0".."9"}
    ),
    // The year appearing in the Forecast Spend columns.
    GetYear_Forecast = Text.Select (
        List.First (
            List.Select (
                FileColumnNames, each Text.Contains ( _, "Forecast Spend", Comparer.OrdinalIgnoreCase ) 
            ) 
        ), {"0".."9"}
    ),
    // Get a list of column names including the word 'Plan' (case non-sensitive), excluding the first.
    DuplicatePlanColumns = List.RemoveFirstN ( 
        List.Select ( 
            FileColumnNames, each Text.Contains ( _, "Plan", Comparer.OrdinalIgnoreCase ) 
        )
    ),
    // Get a list of column names that start with 'Column' (case non-sensitive).
    GenericColumnNames = List.Select ( 
        FileColumnNames, each Text.StartsWith ( _, "Column", Comparer.OrdinalIgnoreCase ) 
    ),
    // Combine duplicate plan columns and generic columns into one list.
    ColumnNamesToRemove = List.Combine ( { DuplicatePlanColumns, GenericColumnNames } ),
    // --------------------------------------------------------
    // Clean up the column names. 
    // --------------------------------------------------------
    // Remove specific columns from the source table.
    RemoveColumns = Table.RemoveColumns ( Source, ColumnNamesToRemove ),
    // Remove numbers (years), parenthesis and leading/trailing spaces.
    TransformedFileColumnNames = Table.TransformColumnNames (
        RemoveColumns,
        each Text.Trim ( Text.Remove ( _, {"0".."9", "(", ")"} ) )
    ),
    // --------------------------------------------------------
    // If they don't already exist, add years columns to the table. 
    // --------------------------------------------------------
    AddYear_Actual = 
        if not Table.HasColumns ( TransformedFileColumnNames, {"Actual Spend"} ) 
        then Table.AddColumn ( TransformedFileColumnNames, "Actual Year", each GetYear_Actual, Int64.Type )
        else TransformedFileColumnNames,
    AddYear_Forecast = 
        if not Table.HasColumns ( AddYear_Actual, {"Forecast Spend"} ) 
        then Table.AddColumn ( AddYear_Actual, "Forecast Year", each GetYear_Forecast, Int64.Type )
        else AddYear_Actual
in
    AddYear_Forecast
in
    fn

Snip of Result