When copying a sales order to a sales invoice or delivery note, any order number will be carried over. So linkage is visible on the destination transaction. But there is no way to tell by looking at the source transaction which or how many forms were copied from it.
When copying a sales order to a sales quote, purchase order, or purchase invoice, the order number is not carried over, because doing so would not make sense in those contexts.
Manager does not prevent multiple copies of transactions for a number of reasons. For example, suppose a sales order includes 10 line items, but they are marked for delivery at separate future dates. You can still copy the sales order to multiple sales invoices, deleting items from each sales invoice that are not being shipped.