Last available date value vs current date value increase or decrease

I added some more sample data to cover more scenarios. It's still not a lot.  Anyway - here is the Power Query.  Any value of 5 and above or -5 and below indicates the streak length.

 

 

let
  fx = (tb) =>
    let
      #"Added Index" = Table.AddIndexColumn(tb, "Index", 0, 1, Int64.Type),
      #"Added Custom" = Table.AddColumn(
        #"Added Index",
        "Flag",
        each
          if [Index] < 5 then
            0
          else
            List.Accumulate(
              {[Index] - 4 .. [Index]},
              0,
              (state, current) =>
                if #"Added Index"[value]{current} > #"Added Index"[value]{current - 1} then
                  state + 1
                else if #"Added Index"[value]{current} < #"Added Index"[value]{current - 1} then
                  state - 1
                else
                  0
            )
      )
    in
      #"Added Custom",
  Source = Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText(
          "fc/NDYAgDIDRXThjAkX8OVrUJQj7ryE1VoJUEumBF8zXGNWm9H2sycPYIX9gwKmko0I2S8NVFtggD/CV7Wzu+ScUO9hGMqjsZPNkvjK6R24ROpF3EDrJVjkTeQUhE98V2szyrs0MnczQyQz/mUSLXEk0y5FE06cxXQ==",
          BinaryEncoding.Base64
        ),
        Compression.Deflate
      )
    ),
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [batch = _t, Product = _t, value = _t, #"purification date" = _t]
  ),
  #"Changed Type" = Table.TransformColumnTypes(Source, {{"purification date", type date}}, "en-GB"),
  #"Changed Type1" = Table.TransformColumnTypes(#"Changed Type", {{"value", Int64.Type}}),
  #"Grouped Rows" = Table.Group(
    #"Changed Type1",
    {"Product"},
    {
      {
        "Rows",
        each _,
        type table [
          batch = nullable text,
          Product = nullable text,
          value = nullable number,
          purification date = nullable date
        ]
      }
    }
  ),
  #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Checked", each fx([Rows])),
  #"Removed Other Columns" = Table.SelectColumns(#"Added Custom", {"Checked"}),
  #"Expanded Checked" = Table.ExpandTableColumn(
    #"Removed Other Columns",
    "Checked",
    {"batch", "Product", "value", "purification date", "Index", "Flag"},
    {"batch", "Product", "value", "purification date", "Index", "Flag"}
  )
in
  #"Expanded Checked"