When an incomplete color contrast is blocked by a background image, there's some additional metadata included in the node result:

nodes: [{
  any: [{
    data: {
      contrastRatio: 0,
      expectedContrastRatio: "3:1",
      fgColor: "#000000",
      fontSize: "36.0pt (48px)",
      fontWeight: "normal",
      messageKey: "bgImage"
    }
  }]
}]

However, when an incomplete color contrast issue is blocked by a pseudo element, the node result's data is mostly empty:

data: {
  messageKey: "pseudoContent"
}

axe-core should still include any additional information that can be reasonably included so that data can be used for other things.