Thankyou muchly :) Looking now. They have unaltered originals too!

There are 3 separate glass slides for the different colour channels. Ooh. (is it healthy to get excited about this?)

EDIT: This collage of the 3 coloured slides is itself an edited version, but it shows answers to my questions:

They edited the left side with a clone tool to hide the fact some of the coloured slides/layers are a bit faded at the edges. This also explains why the left of the image is yellowish and the bottom reddish. Perhaps those slides were like that their entire life, uneven due to manufacture or developing issues?

Across the entire image are tiny coloured blips and scratches. Most of them were edited out.

The rounded shape of the chroma on the flowers isn't as evident in this version, but it still looks blurry. It's plausible it's an artefact from multiple lossy image encodings POSSIBLY combined with the red channel (glass slide) having worse resolution than the other colours in these areas (?).