Each bike comes with an Item ID, so that you can easily find it and see which bikes are rented out.
BRM does go to great lengths to ensure that your Item IDs are unique, but it can happen that you get duplicates - this should be fixed as soon as possible if you ever spot a duplicate.
If you have any items not yet named you can go ahead and name them directly from the inventory shape page:
Q. Can you change the ID of your Items? (even if you have live reservations)
YES - you can. BRM has an internal identifier for each bike (which really is unique) so you can feel free to change your Item ID's
Simply go to the Item Id field and write in your new ID, hit Save
Q. Can the Bardcode be different?
YES - it can. When you name an Item it is given the same barcode by default, but then you can make them different if necessary.