Based on what I saw in the various failure pictures, it seems to me this was a design problem not a manufacturing problem; if this is correct it therefore affects ALL Terns made before the weld design was changed and augmented, ... (snip) ? ...
The design problem was no weld in line with the frame yes? Solution was adding the gusset plate. What about other bikes with mid fold hinges? Crius, Fnhon, Dahon etc. Did they do it right?