Historical Log support

A different method, using GroupKind.Local:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("fZI7DoNADESvEm2NBPZ+3aenSYe4/zWCtIHsZ+wCIb0ngzye43CpiFvc63qIVlp5Y3bn0nFWeMV+wIyxxzhgHGf82d9E1zvhiYxxwVgwpk3hyq4/HHAEI/YzvpcKeCJinPQPZV0VXYmu7kigA/s/DoTwuKoijq1iFi7gVwwlW7I93eDYcN5wwXARuOZocCYbrhhODNd3WYkTy/ZyODHovOGC4SJwU83/MzLWvFdFV6KrvuaDUwKRqeaDw32WrurnFw==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Store = _t, #"PCC Support" = _t, #"Reporting Month" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{
        {"Store", Int64.Type}, {"PCC Support", type text}, {"Reporting Month", type date}}),
    
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Store","PCC Support"}, {
        {"Start", each List.Min([Reporting Month]), type nullable date},

    //Assuming "Last reporting month" is the month preceding the current month
        {"End", each [a=Date.EndOfMonth(List.Max([Reporting Month])),
                      b=Date.IsInPreviousNMonths(a,1),
                      c=if b then null else a][c],        
         type nullable date}},
        GroupKind.Local),
    
    #"Filtered Rows" = Table.SelectRows(#"Grouped Rows", each ([PCC Support] <> " "))
in
    #"Filtered Rows"