Customer Forecasts: Calculating latest value when a record removed from most recent data source

I put the below together with the following embellished test data:

CombinedWorkbooks

Same as your data, BB22 is missing a File C record.

The following code will figure out the expected latest file for each delivery date, then use that to either pull latest order record when from latest file, or construct a 0 Qty order from latest file if no such order exists.

let
    Source = CombinedWorkbooks,

    // Latest related file for each delivery date based on all products
    ExpectedDates = Table.ExpandRecordColumn( 
        Table.Group( 
            Table.Sort( Source, { "File Received Date", Order.Descending } ), 
            "Delivery Date", {
                "MaxFileRow", Table.First, 
                Type.TableRow(Value.Type(Source))
            }
        ), 
        "MaxFileRow", {"FileName","File Received Date"} 
    ),

    // For each Product and Delivery Date:
    GroupAndAddMissing = Table.Group( 
        Source, {"Product Code", "Delivery Date"}, 
        { { 
            "groups", 
            each [ 
                // Get latest order within the group
                LatestOrder = Table.First( Table.Sort( _, {"File Received Date", Order.Descending} ) ), 
                // Get latest expected file for the delivery date (using ExpectedDates table)
                LatestFile = Table.First( 
                    Table.SelectRows( ExpectedDates, each [Delivery Date] = LatestOrder[Delivery Date] ) 
                ), 
                // Does latest file for this order match latest expected file?
                DatesMatch = LatestFile[File Received Date] = LatestOrder[File Received Date],
                // If latest order is from latest file, use it as is.
                // Otherwise, return a row from latest file with 0 Qty order
                ResultRow = 
                    if DatesMatch then 
                        LatestOrder 
                    else 
                        LatestFile & [ Product Code = LatestOrder[Product Code], Qty = 0 ]
            ] [ResultRow], 
            Type.TableRow( Value.Type( Source ) )
        } } 
    ),
    
    Combine = Table.FromRecords( GroupAndAddMissing[groups], Value.Type( Source ) )
in
    Combine

Result: