So I ended up picking up a Pacific Blue FineWoven (official) to go along with my knockoff Ali Express green one. I thought I'd take some macro shots and compare the construction of the two. With both side by side, it's easy to see which is the knockoff, but without reference, it's much harder. For the record, I really like the finewoven cases...they look really nice, IMO (especially the blue), and I like the feel too. I'm generally not too rough on my cases, so hopefully mine stays in decent condition. So far no permanent marks through 2.5 days.
Key differences:
1) The official FW case is a fair bit thinner than the knockoff, presumably because of the microfiber lining used rather than just having FW fabric on the inside like the official case.
2) The woven/coated weave at the edges is different, with the official having more coating and less visible fibers.
3) The buttons on the knockoff are thinner and not as precicely cut as the official buttons, though they work fine.
4) The apple logo is accentuated differently, with the knockoff having much more defined edges.
Surprisingly, the weave is actually very similar between the two, as is the feel in the hand.
Some shots comparing the two. Green is AliExpress knockoff, Blue is official Apple. (for those interested, taken with the Nikon Z8 and MC 105mm f/2.8 VR S macro:
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Sides w/ buttons. Can see the button size difference, the difference in edge weave and the thickness difference.
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Closeup of the finewoven fabric:
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