Missing barcodes at stocktake

In the process of completing our stocktake we discovered a number of books from which the barcodes had “mysteriously” vanished. I was wondering if there was a way to change the barcodes on OASIS and so allocate a new barcode to the book or if I need to dispose of the books and accession them again.
 
Just one thing, Jennifer and anyone else in this same predicament.. If you have initialized a section you should not change the barcode until after you have finalized. If a barcode is missing  look it up and write it in the book somewhere. Then enter the barcode in B2-H3. Only after finaiizing do you change it.