What are the requirements (if any) with regards to reporting credit bureau information for authorized signers on loans to businesses?

Should we report to the credit bureaus information on someone only if they are guaranteeing the loan?

We have numerous LLC loans in which there is an authorized signer. Most have sole owners.

We use Fiserv as our core processor. They report to the bureaus first on the primary TIN (the business) then on any secondary TINs (the authorized signer).

I don't know about the requirments but I do know that Equifax strips off all loans to business entities, including the comakers, guarantors, signers, etc. even if you send them. TransUnion strips the business name but reports the guarantors, comakers, etc. Experian hasn't responded to our inquiry yet.

I just learned that we do not report commercial loans to the credit bureau. Is this a common banking practice?

I think it is very common. I have never worked for a bank that did report them.