Discussed with @fanf2 on the topic of additional section processing:
Additional section processing for resolvers may be slightly different than the processing that happens on the authoritative.
Target address records likely not needed in additional section: When an authoritative server receiving an address query just the ANAME should go in the additional section: The (already expanded) sibling address records need to go in the answer section.
The terminology with respect to target records can be improved: What is a target record, does it include the owner name or is it just the RDATA? Perhaps we need split up the definitions into target record and target RDATA.
Discussed with @fanf2 on the topic of additional section processing: