Continuing to search for related topics, I stumbled upon the Advanced Test feature under Emails in Admin. I suspected this would be the thing doing it but using that feature, I confirmed that it is the trim incoming emails setting causing this, described as Trim part of the incoming emails that isn't relevant.
With that setting turned off, I get the correct results for those emails but rebaking doesn’t appear to reprocess the emails so the question remains: How do I tell Discourse to reprocess posts from their incoming emails?