My suggestion is:

• the certified party

Once the person or entity has requested or applied for some certification, it may hold a certificate or may have been conferred some certification or attestation.

I think "certified party" is wide enough to cover any such meanings.

My suggestion is:

• the certified party

Once the person or entity has requested or applied for some certification, they may hold a certificate or may have been conferred some certification or attestation.

I think "certified party" is wide enough to cover any such meanings.