My recent renewal arrived about 6 weeks after my anniversary date. Mine came ordinary US first-class US mail. There was no tracking number attached to it, so I doubt that (ISC)² could track it after it left their door. If it has been over 8 weeks, contact member services so they can send a replacement.
Given the low economic value, it is probably cheaper to ship without extra-cost options and send a replacement in the few cases where it gets lost.
@Cybertron I'm sorry to hear you have not received your certificate yet. Please email me directly with your primary email address and member ID and I will look into when the package was sent. It is true we do not have tracking on the certificate packages, but if it's been up to 12 weeks from your cycle start date, we can look into a replacement.