This backrest is used and original from Herman Miller chair. The photos are from one of 5 backrests I have. Happy to send photos/video before sending it.
Please note slight damage: in one spot (front right when looking at chair) the seat has a some of the threads missing in the fabric as shown in close-up in the third photo. Many of the threads remain in place in that spot and it’s not a “hole” – it’s more that some of the interweaved fabric is worn out. Plus several markings/signs of use/wear (nothing that affects the operation of the chair). This chair is priced lower due to the small damage.