I checked this UR5e order by complete kit contents after my earlier finger-count muddle, and the spare cable is definitely missing although the fitted cable is present; seller agrees it is owed but keeps saying it will follow another shipment
Also ask maintenance how urgent the spare is for your handover. That won't settle the shortage, but it stops somebody assuming the shelf is ready because the installed cable works.
Maintenance has it listed as absent now, Reece, and seller offered credit instead of separate supply, but the amount is less than the compatible replacement quote I obtained