Credited On vs. Also Performs On

What distinguishes who gets to be a “Credited On” vs. an “Also Performs On” in the credits for an album? Here’s just one of many examples that annoy me. On The New National Anthem album by Riverside, Dave Douglas (trumpet), Chet Doxas (clarinet/saxophone), Steve Swallow (bass), and Jim Doxas (drums) all play on all 11 tracks. I have entered all four names for each track (roon’s crack metadata sources must not have had any artists for this album although it is identified). Yet just Douglas and Swallow are “Credited On”; the poor Doxas brothers get relegated to “Also performs” (and get smaller circles for their misaligned photographs).