Thanks for the input everybody! After spending another two hours or so staring at these shoes I'm pretty convinced that
septic and
joberg are right and that the ridge is actually the edge of the material used to reinforce the eyestay. (I think it's called "eyestay" anyway, I mean the bit with the eyelets the laces normally go through.)
I think you can make out at least two layers in the reinforcing material and it looks thicker than other examples of PF Flyers I could find online so I'm thinking costuming might have added additional reinforcing layers to the eyestay themselves. Here's the layers:
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And here are some 1960s PF Flyers I found online for comparison, note how thin the eyestay reinforcing material is on these compared to Ripley's shoe:
View attachment 1545988View attachment 1545989
(On that note, I think they might have removed the hemming around the topline of the shoe. There should be a pretty distinct straight shadow there where the hem normally is but instead that part is just flat and so thin that the ridges of the socks are showing through. Really not sure on that one, though.)
For what it's worth, Dallas' shoe seems to be either option 1 or 2 - either the eyestay is one layer below the rest of the fabric making up the shoe, or the eyestay and the rest of the fabric are one continuous piece of fabric with an additional thin strip of fabric sewn on top as a sort of bias tape. So
Banzai88 is also sort of correct!
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