Updating table rows based on earlier row

I'm sorry, I'm not sure I understand the question. 

If a record has "[Flag] = "Adj" and [Case] = "L", I want to set [Output] ="H" for all other records with the same [ID] where [Date] > than the date value contained in this record and where [Case] != "L"".

The second part of the logic ([Case] != "L") is because eventually the golden source will update and a record will be ingested containing x.[ID], x.[Case] and [Flag] = Source.

Hopefully this helps clarify?

Someone else suggested the below to me:

let
    Source = Table.Sort(your_table, {"ID", "Date"}),
    rec = (x) => [L = {"Output", each "H"}, M = {"Level", each x{0}[Level]}],
    fx = (tbl) => Table.TransformColumns(tbl, Record.FieldOrDefault(rec(tbl), tbl{0}[Case], {})),
    group = Table.Group(
        Source, 
        {"ID", "Case"},
        {"x", fx},
        GroupKind.Local, 
        (s, c) => Number.From(s[ID] <> c[ID] or List.Contains({"L", "M"}, c[Case]))
    ),
    z = Table.Combine(group[x])
in
    z

This seems to achive close to the outcome I'm looking for, although I suspect for performance optimisation, it would be better to execute this as a step within the existing query, rather than a standalone. Additionally, the outputs seem slightly different from what I'm expecting. I wonder if it's because the flag logic isn't considered and the rules are applied to all records regardless.

If you have any thoughts on how to update to achieve the correct output, I'd be greatly appreciative.

Thanks