Sequential Assigned Number

Does the numbering have to start at 1?

Table Stores:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjQyN7E0U9JRcgRiQ6VYHSQhJyA2QhVyBmJjVCEXIDaBCBmbmJuZArmuCLNgQm4Is2BC7gizYEIemGZ5ArGpUmwsAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Store = _t, Employee = _t, #"Employee #" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Store", Int64.Type}, {"Employee", type text}, {"Employee #", Int64.Type}})
in
    #"Changed Type"

Table Orders:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("Zc+7EcQwCEXRXhQ7ED+BavG4/zbs8WywXKdn4D04z1GS4xii6XuN63hAq4PL6mBzdogvKAEtYWgJ5R2xO2TwjnCAo9Zz8TmsbEFLCX5xfTPsyYrfhHZID4BiIswBCys70KI5AQKoOXkHMswLwIzN51I5UTi97H/lugE=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"order #" = _t, Store = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"order #", Int64.Type}, {"Store", Int64.Type}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Counter", (k)=> Table.SelectRows(Stores,each [Store]=k[Store])),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Custom", each 1+Number.Mod([Index],Table.RowCount([Counter]))),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom1",{"order #", "Store", "Custom"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Removed Other Columns",{{"Custom", Int64.Type}})
in
    #"Changed Type1"

These are Power Query queries. How to use this code: Create a new Blank Query. Click on "Advanced Editor". Replace the code in the window with the code provided here. Click "Done".

If the seqence has to start at 1 then the Orders table would be slightly different:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("Zc+7EcQwCEXRXhQ7ED+BavG4/zbs8WywXKdn4D04z1GS4xii6XuN63hAq4PL6mBzdogvKAEtYWgJ5R2xO2TwjnCAo9Zz8TmsbEFLCX5xfTPsyYrfhHZID4BiIswBCys70KI5AQKoOXkHMswLwIzN51I5UTi97H/lugE=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"order #" = _t, Store = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"order #", Int64.Type}, {"Store", Int64.Type}}),
    AddCount = (t as table)=> let
    #"Added Index" = Table.AddIndexColumn(t, "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Counter", (k)=> Table.SelectRows(Stores,each [Store]=k[Store])),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Custom", each 1+Number.Mod([Index],Table.RowCount([Counter])))
     in
    #"Added Custom1",
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Store"}, {{"Count", each _, type table [#"order #"=nullable number, Store=nullable number]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Custom", each AddCount([Count])    ),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom",{"Custom"}),
    #"Expanded Custom" = Table.ExpandTableColumn(#"Removed Other Columns", "Custom", {"order #", "Store", "Index", "Counter", "Custom"}, {"order #", "Store", "Index", "Counter", "Custom.1"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Expanded Custom",{"order #", "Store", "Custom.1"})
in
    #"Removed Other Columns1"