A certification is a formal declaration that you have met or exceeded a minimum standard of knowledge on a subject on a particular exam day. It doesn't mean that you will retain the information forever, nor that you will update your knowledge after receiving the certification.
I have an A+ from 2005. Officially, it is a "good for life" certification that I am not required to update. But a lot has changed since then. I tested on DOS, Windows 9x, Windows 2000, and Windows XP. We're up to Windows 10 and 11. Virtualization, the cloud, and IoT devices weren't on the exam back then, but they are now. I have passed three other versions of A+ since then.
Do I possess the knowledge to teach A+ for the current version of the exam? There is no guarantee. A lot of the information from the previous exams will still be valid but some of it has changed or is brand new. I'd have to study to make sure my knowledge is current enough to teach the current objectives.
An A+ cert by itself doesn't tell you if someone is sufficient to teach a course. You'll need more information to determine if the instructor is ready to teach the current version.