Adding domains to and deleting domains from existing certificate

I don't know what a SANs list is. Please explain or point me to appropriate documentation, much appreciated.

How is it that something "needs fixing" when it's been running perfectly for years.

This is from the debug toolkit. Now looks like I have four certificates with overlap. I fully do not know what's going on, what if anything needs to be changed.:

Found 4 certificates issued.

Rate Limit Status

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Rate Limit Status
Certificates per Registered Domain The Registered Domain (sme62.org) has used 0 of 50 weekly certificates.

Due to changes in how Let's Encrypt applies the renewal exemption, this calculation is no longer accurate (overestimating how close a domain is to this rate limit) and is unlikely to be fixed.|
|Duplicate Certificates||
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Certificates