According to this review article, for symptomatic internal carotid artery stenosis:
[Carotid endarterectomy] was highly beneficial in participants with 70% to 99% stenosis without near-occlusion (N = 1095, RR 0.47, 95%CI 0.25 to 0.88). However, there was no evidence of benefit (N = 271, RR 1.03, 95%CI 0.57 to 1.84) in participants with near-occlusions
Why is carotid endarterectomy beneficial for 70%-99%, but not 100% stenosis (unsure if this is the correct term)?
Source: Orrapin S, Rerkasem K. Carotid endarterectomy for symptomatic carotid stenosis. Cochrane Database Syst Rev. 2017 Jun 7;6(6):CD001081. doi: 10.1002/14651858.CD001081.pub3. PMID: 28590505; PMCID: PMC6481587.