Ink sport - or not?

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Initially, when I saw this note, I thought it was just a typical oil stain. But when I looked closer I saw that the initially perceived "soiling" had not penetrated the front & other irregularities which made me reassess the entire note more closely. Although it looks in rough shape it is actually close to VF, still quite crisp with sharp edges/corners.

Inspecting the front I noticed a dark border which runs vertically (& narrowly) across the top margin (above "CANADA"). There appears to be a broader similar border (defect) which runs on the reverse (possible ink spot) side. It is only very slightly noticeable and appears to run below "CANADA." The discolouration appears to be exactly the same colour as the background trees. These CBN notes don't have the sheen that the old AAT (& earlier BAI) notes had so it is hard to discuss/describe the paper quality (esp where the discolouration occurs.

Any thoughts? Does it appear to be an error or manufactured (stained) note?