Dynamically select and merge columns while retaining others

Hi Insert_Key 

The problem comes from:

Select Label Columns = Table.SelectColumns(Source, #"List Label Columns")

You don't need to do that. Instead, simply pass the list of columns to merge (List Label Columns) to the step where you merge the columns - line 8 below. Something like:

let
    Source = ...,
    SourceNames = Table.ColumnNames( Source ),
    ListLabelColumns = List.Select( SourceNames, each
        Text.StartsWith(_, "Labels")
    ),
    MergedLabelColumns = Table.CombineColumns( Source,
        ListLabelColumns,
        Combiner.CombineTextByDelimiter(" ", QuoteStyle.None),
        "MERGED LABELS"
    ),
    Result = if List.Count(ListLabelColumns) < 2
             then Source
             else MergedLabelColumns
in
    Result