Notice of cancellation
Advance notice that a contractor's policy is being cancelled. The certificate itself doesn't promise to tell you.
ACORD 25On the certificate
The current ACORD 25 says notice will be delivered in accordance with the policy provisions. That is a pointer to the policy, not a promise to the certificate holder.
What to check
If your contract requires notice to you, an endorsement on the policy that names you to receive it, and a process to recheck certificates before they expire.
The common gap
Relying on a certificate from the start of the job. A policy can be cancelled for nonpayment mid-project and the certificate in your file still looks fine.
Go deeper on forsured.ai: Will a COI tell you if a contractor's policy is cancelled?
Related: Certificate of insurance · Per project aggregate · Try Spot the Gap
General information, not legal or insurance advice. Ask your broker what your policies actually carry.