Because 99.9% of the trades are done electronically and MM's are the ones that are required to report, little enforcement is needed.
Fails to deliver are electronically-trackable, too. If there were significant fails-to-deliver, then there possibly would be concerns about naked shorting (there are no concerns)
Often, the short interest reported can simply be the leftover short volume on the reporting day, which is often covered within seconds or minutes.
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