The correct way to add several copies of a resource that will be stored in the same place (ie. together) is to add one catalogue entry and then add several barcodes to the record
If you have found several entries that really should be made one there is a way to do this easily
*** You must MOVE the highlighter to access the buttons
Then this screen appears ready for you to decide what to do next... and as the NOTE: just bellow the buttons suggests, the BOLD record in the list is the record you were sitting on when you pressed <F8>... just in strange words!
(The second item is highlighted because I clicked on it just before taking a picture of the screen)
(You can always go into the deleted record, un-delete it and do the move again in the other direction if you mess it up! You might like to check out the Move Barcode function also... which is No. 17 on the Menus, Toolbars and Shortcut keys page!)