“Defect” implies a necessary response. A defective product is a product that a manufacturer is legally obligated to repair, replace, or refund. A “defect notice” is thus a notice that the manufacturer is legally obligated to remediate the problem.
It is also consistent with existing terminology, see: “Most decisions to conduct a recall and remedy a safety defect”. We see that the “recall” refers not to the remedy, but to the notice that the manufacturer has obligations to remedy the defect.
Note that “mandatory safety update” is also incorrect because:
“Manufacturers are required to fix the problem by repairing it, replacing it, offering a refund, or in rare cases repurchasing the vehicle.”
So, a update is not necessary, it is usually just the cheapest option which is why it is the most common. Also note how the remediations proposed are consistent with standard defect remediation as I laid out above.