let
    Source = Excel.CurrentWorkbook(){[Name="Таблица1"]}[Content],
    Split = Table.SplitColumn(Source, "Столбец1", Splitter.SplitTextByDelimiter("/", QuoteStyle.Csv), {"c", "d"}),
    Index = Table.AddIndexColumn(Split, "Индекс", 0),
    Changed = Table.TransformColumnTypes(Table.TransformColumns(Index,{{"Столбец2", each _&".2018"}}),{{"Столбец2", type date}}),
   Index1 = Table.AddIndexColumn(Changed, "Индекс.1", 1),
    Merged = Table.NestedJoin(Index1,{"Индекс.1"},Index1,{"Индекс"},"b",JoinKind.LeftOuter),
    Expanded = Table.ExpandTableColumn(Merged, "b", {"Столбец2"}, {"Столбец2.2"}),
    Custom1 = Table.AddColumn(Index, "a", each if [Индекс] <= List.Min( List.RemoveLastN(Table.AddColumn
    (Expanded, "a", each if [Столбец2.2] < [Столбец2] then [Индекс] else null)[a],1)) then [c] else [d]),
    Merged1 = Table.CombineColumns(Custom1,{"Столбец2", "a"},Combiner.CombineTextByDelimiter(".", QuoteStyle.None),"b"),
    Changed1 = Table.TransformColumnTypes(Merged1,{{"b", type date}})[[b]]
in
    Changed1

let
    Source = 
        Excel.CurrentWorkbook(){[Name="Таблица1"]}[Content],
    Grouped =
        Table.Group(
            Source, 
            {"Столбец2"}, 
            {{"a", each _, type table}},
            0,
            (a,b)=>let c=(s)=>Number.From(Text.AfterDelimiter(s,".")) 
                   in Number.From(c(b[Столбец2])<c(a[Столбец2]))
        )[a],
    fn=(i)=>
        Text.Split(Grouped{0}{0}[Столбец1],"/"){i},
    Transformed = 
        List.Generate(()=>
            [i=0,year=fn(i)],
            each [i]<List.Count(Grouped),
            each [i=[i]+1,year=fn(i)],
            each 
                let 
                    year=[year], 
                    addyear=Table.TransformColumns(Grouped{[i]},{{"Столбец2", each Date.From(_&"."&year)}}) 
                in Table.TransformColumnTypes(addyear,{{"Столбец2",type date}})),
    Combined = 
        Table.Combine(Transformed)
in
    Combined