Filling Data Gaps, Conditionally

Thanks Phil_Seamark

Otherwise this would be my solution in this case (in which your table creation is copied with pride):

let
    // These steps are to create the initial table
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("VY+7DcAgDAVXsagjgfmFlCFjIPZfIxI2PKC8M2e5NfMSsWXrHWeiQuN50y81Xg07ItCg9Jb5ABPV5IHqHk8ynGBmPIrZ/swFBegsf0cZaCYfSTJMOJaBr+66vf8=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Column1 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column1", type text}}),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Changed Type","Column1",Splitter.SplitTextByDelimiter(" ", QuoteStyle.Csv),{"Column1.1", "Column1.2", "Column1.3", "Column1.4", "Column1.5", "Column1.6", "Column1.7", "Column1.8", "Column1.9", "Column1.10", "Column1.11"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"Column1.1", type text}, {"Column1.2", type text}, {"Column1.3", type date}, {"Column1.4", type text}, {"Column1.5", Int64.Type}, {"Column1.6", type text}, {"Column1.7", type text}, {"Column1.8", type text}, {"Column1.9", type text}, {"Column1.10", type text}, {"Column1.11", Int64.Type}}),
    #"Removed Columns" = Table.RemoveColumns(#"Changed Type1",{"Column1.2", "Column1.4"}),
    #"Reordered Columns" = Table.ReorderColumns(#"Removed Columns",{"Column1.1", "Column1.3", "Column1.5", "Column1.7", "Column1.8", "Column1.9", "Column1.6", "Column1.10", "Column1.11"}),
    #"Removed Columns1" = Table.RemoveColumns(#"Reordered Columns",{"Column1.7", "Column1.8", "Column1.9", "Column1.6", "Column1.10"}),
    #"Renamed Columns" = Table.RenameColumns(#"Removed Columns1",{{"Column1.11", "Fillcol"}, {"Column1.1", "Column1"}}),

    // Now we have the initial table, we add 2 indices to join the table with itself,
    // such that the previous Column1 value will be on the same row as the current Column1 value
    #"Added Index" = Table.AddIndexColumn(#"Renamed Columns", "Index", 0, 1),
    #"Added Index1" = Table.AddIndexColumn(#"Added Index", "Index.1", 1, 1),
    #"Merged Queries" = Table.NestedJoin(#"Added Index1",{"Index"},#"Added Index1",{"Index.1"},"Previous",JoinKind.LeftOuter),
    #"Expanded Previous" = Table.ExpandTableColumn(#"Merged Queries", "Previous", {"Column1"}, {"Previous.Column1"}),
    #"Sorted Rows" = Table.Sort(#"Expanded Previous",{{"Index", Order.Ascending}}),

    // If first row for Column1 value is null, then replace with "" to block the filldown
    #"Added Custom" = Table.AddColumn(#"Sorted Rows", "NewFillcol", each if [Fillcol] = null and [Column1] <> [Previous.Column1] then "" else [Fillcol], Int64.Type),
    #"Filled Down" = Table.FillDown(#"Added Custom",{"NewFillcol"}),

    // Now turn the "" back to null
    #"Replaced Value" = Table.ReplaceValue(#"Filled Down","",null,Replacer.ReplaceValue,{"NewFillcol"}),

    // Finishing touches
    #"Removed Columns2" = Table.RemoveColumns(#"Replaced Value",{"Fillcol", "Index", "Index.1", "Previous.Column1"}),
    #"Renamed Columns1" = Table.RenameColumns(#"Removed Columns2",{{"NewFillcol", "Fillcol"}})
in
    #"Renamed Columns1"