Append new Excel table into dataset without loading again old data?

Hi everyone,

I've read a few topics on how to append data in PBI but still find it very slow/

So I have a large number of excel files like below and I imported into PBI via folder import (code as below).

EAch month when I have a new file (which basically is monthly volume sales), I tried to put in the same folder and refresh the query. But I see it loaded again from Jan'17 file until the latest month data...which is an EXTREMELY SLOW process...and sometimes it just froze like forever....

I have pasted my query below to get the data from folder.

My query:

let
    Source = Folder.Files("E:\DMS EMS\SALES BY CUSTOMER SKU\2017\HCMP"),
    #"Added Custom" = Table.AddColumn(Source, "Custom", each Excel.Workbook([Content],true)),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Extension", "Date accessed", "Date modified", "Date created", "Attributes", "Folder Path"}),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Removed Columns", "Name", Splitter.SplitTextByDelimiter("_", QuoteStyle.Csv), {"Name.1", "Name.2", "Name.3"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"Name.1", Int64.Type}, {"Name.2", type text}, {"Name.3", type text}}),
    #"Removed Columns1" = Table.RemoveColumns(#"Changed Type",{"Name.3"}),
    #"Renamed Columns" = Table.RenameColumns(#"Removed Columns1",{{"Name.2", "Location"}}),
    #"Split Column by Position" = Table.SplitColumn(Table.TransformColumnTypes(#"Renamed Columns", {{"Name.1", type text}}, "en-GB"), "Name.1", Splitter.SplitTextByPositions({0, 4}, false), {"Name.1.1", "Name.1.2"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Split Column by Position",{{"Name.1.1", Int64.Type}, {"Name.1.2", Int64.Type}}),
    #"Renamed Columns1" = Table.RenameColumns(#"Changed Type1",{{"Name.1.2", "Month"}, {"Name.1.1", "Year"}}),
    #"Expanded Custom" = Table.ExpandTableColumn(#"Renamed Columns1", "Custom", {"Name", "Data", "Kind"}, {"Name", "Data", "Kind"}),
    #"Filtered Rows1" = Table.SelectRows(#"Expanded Custom", each ([Kind] = "Sheet")),
    #"Expanded Data" = Table.ExpandTableColumn(#"Filtered Rows1", "Data", {"LocalSalesRegionLevel4", "LocalSalesRegionLevel4Name", "CustomerCode", "CustomerName", "OutletCode", "OutletName", "SalesRouteCode", "SalesRouteName", "SalesRouteType", "ContactName", "PhoneNumber", "Address1", "Address2", "Address3", "TerritoryL4", "TerritoryL4Name", "OutletLevel2", "Visicooler", "PepsiClub", "AnchorAccount", "CreatedDate", "Level2Code", "Level2Name", "ProductCode", "ProductName", "OrderQuantity", "OrderCount", "VisitPlan"}, {"LocalSalesRegionLevel4", "LocalSalesRegionLevel4Name", "CustomerCode", "CustomerName", "OutletCode", "OutletName", "SalesRouteCode", "SalesRouteName", "SalesRouteType", "ContactName", "PhoneNumber", "Address1", "Address2", "Address3", "TerritoryL4", "TerritoryL4Name", "OutletLevel2", "Visicooler", "PepsiClub", "AnchorAccount", "CreatedDate", "Level2Code", "Level2Name", "ProductCode", "ProductName", "OrderQuantity", "OrderCount", "VisitPlan"}),
    #"Filtered Rows" = Table.SelectRows(#"Expanded Data", each ([Kind] = "Sheet")),
    #"Removed Columns2" = Table.RemoveColumns(#"Filtered Rows",{"Content", "Kind", "Name", "LocalSalesRegionLevel4"}),
    #"Changed Type2" = Table.TransformColumnTypes(#"Removed Columns2",{{"CreatedDate", type datetime}, {"OrderQuantity", type number}, {"OrderCount", type number}})
in
    #"Changed Type2"

My excel have table header like below, These stay the same,

but some months there were extra but unnecessary headers.