Regarding the 18th AF, snip a piece of the white bobbin thread off the back and burn test it. If it burns quickly with an ashy residue and burnt hair like smell, it is ok.
If it burns into a tiny hard ball and smells of burnt plastic, it is bad.
I ask this as the appearance of the white bobbin thread on back is typical of the fake patches; slightly different from the almost off white snowy appearance of cotton thread. The burn test will verify however.
CB
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