item tracking. importing serial nos from external system

Hi,

Not an expert on item tracking here :-)

External system assigns serial numbers to Purchase Order Lines via BC extension method (see code below)
Sometimes, purchase order line already has the serial numbers assigned and they could be the same as those in external system.

External system does not know about it and still tries to assign serial numbers.

As a result, quantities in the tracking lines are wrong:



Instead it should be without undefined quantity:



How can you find if serial number already exists in the item tracking to skip it during the process of importing serial nos from external system?
Where is this information stored?

procedure AssignSerialNos(DocumentType: Integer; DocumentNumber: Code[20]; LineNo: Integer; SerialNosString: Text) Assigned: Boolean;
    var
        Item: Record Item;
        PurchaseHeader: Record "Purchase Header";
        PurchaseLine: Record "Purchase Line";
        ReservationEntry: Record "Reservation Entry";
        TrackingSpecification: Record "Tracking Specification";
        CreateReservEntry: Codeunit "Create Reserv. Entry";
        ItemTrackingMgt: Codeunit "Item Tracking Management";
        ItemTrackingPage: Page "Item Tracking Lines";
        TrackingLinesInitialized: Boolean;
        i: Integer;
        SerialNosList: List of [Text];
        RunMode: Enum "Item Tracking Run Mode";
    begin
        SerialNosList := SerialNosString.Split(';');
        if SerialNosList.Count = 0 then
            exit(false);

        PurchaseHeader.Get(DocumentType, DocumentNumber); //DocumentType:Order=1,Invoice=2,CreditNote=3        
        case PurchaseHeader."Document Type" of
            PurchaseHeader."Document Type"::Order:
                PurchaseLine.Get(PurchaseHeader."Document Type"::Order, PurchaseHeader."No.", LineNo);
            PurchaseHeader."Document Type"::Invoice:
                PurchaseLine.Get(PurchaseHeader."Document Type"::Invoice, PurchaseHeader."No.", LineNo);
        end;

        PurchaseLine.TestField(Type, 2); //2 = item            
        PurchaseLine.TestField("No.");
        PurchaseLine.TestField("Quantity (Base)");

        Item.Get(PurchaseLine."No.");
        Item.TestField("Item Tracking Code");

        ReservationEntry.Reset();
        ReservationEntry.SetRange("Source Type", DATABASE::"Purchase Line");
        ReservationEntry.SetRange("Source Subtype", PurchaseLine."Document Type");
        ReservationEntry.SetRange("Source ID", PurchaseLine."Document No.");
        ReservationEntry.SetRange("Source Ref. No.", PurchaseLine."Line No.");
        ReservationEntry.SetRange("Source Batch Name", '');
        ReservationEntry.SetRange("Source Prod. Order Line", 0);
        If NOT ReservationEntry.IsEmpty then begin
            ReservationEntry.DeleteAll(true);
        end;

        For i := 1 to SerialNosList.Count do begin
            ReservationEntry."Serial No." := SerialNosList.Get(i);

            if PurchaseLine."Document Type" = PurchaseLine."Document Type"::Order then begin
                CreateReservEntry.CreateReservEntryFor(
                    DATABASE::"Purchase Line",   //ForType
                    1,                           //ForSubtype - Order
                    PurchaseLine."Document No.", //ForID
                    '',                          //ForBatchName
                    0,                           //ForProdOrderLine
                    PurchaseLine."Line No.",     //ForProdOrderLine
                    1,                           //ForQtyPerUOM
                    1,                           //Quantity
                    1,                           //QuantityBase
                    ReservationEntry);           //ForReservEntry            
            end;

            if PurchaseLine."Document Type" = PurchaseLine."Document Type"::Invoice then begin
                CreateReservEntry.CreateReservEntryFor(
                    DATABASE::"Purchase Line",   //ForType
                    2,                           //ForSubtype - Invoice
                    PurchaseLine."Document No.", //ForID
                    '',                          //ForBatchName
                    0,                           //ForProdOrderLine
                    PurchaseLine."Line No.",     //ForProdOrderLine
                    1,                           //ForQtyPerUOM
                    1,                           //Quantity
                    1,                           //QuantityBase
                    ReservationEntry);           //ForReservEntry            
            end;

            CreateReservEntry.CreateEntry(
                PurchaseLine."No.",
                PurchaseLine."Variant Code",
                PurchaseLine."Location Code",
                PurchaseLine.Description,
                PurchaseLine."Expected Receipt Date",
                0D,
                0,
                ReservationEntry."Reservation Status"::Surplus);
        end;

        // item tracking lines have to be synchronized between sales and purchase orders, when the purchase order is a drop shipment
        If PurchaseLine."Drop Shipment" then begin
            If not TrackingLinesInitialized then begin
                //PurchLineReserve.InitTrackingSpecification(PurchaseLineLoc,TrackingSpecification);
                TrackingSpecification.InitFromPurchLine(PurchaseLine);
                ItemTrackingPage.SetRunMode(Runmode::"Drop Shipment");
                IF PurchaseLine."Sales Order No." <> '' THEN
                    ItemTrackingPage.SetSecondSourceRowID(ItemTrackingMgt.ComposeRowID(DATABASE::"Sales Line", 1, PurchaseLine."Sales Order No.", '', 0, PurchaseLine."Sales Order Line No."));
                ItemTrackingPage.SetSourceSpec(TrackingSpecification, PurchaseLine."Expected Receipt Date");
                TrackingLinesInitialized := true;
            end;
            ItemTrackingPage.SynchronizeLinkedSources('')
        end;
    end;