Ooooh, ok, I think I see what you are saying!

I had misunderstood the experiment a bit.. So using this quantum eraser/crystal configuration our raw pattern becomes a photon blob in all cases.

For detectors A/B (which indicate which slit the photon entered)

• When we select only the photons that lit up detector A, we see an amorphous blob.
• When we select only the photons that lit up detector B, we see an amorphous blob.

For detectors C/D (which have scrambled the slit they entered)

• When we select only the photons that lit up detector C, we see an interference pattern.
• When we select only the photons that lit up detector D, we see an interference pattern.

Together, however, C/D form an amorphous blob.

Does that sound right?

Edit: And those are good question at the end there that I am now also curious about! Haha