There are specialty manufacturers that make various parts for loudspeaker drivers, and when ordering specialty drivers it is possible for a manufacturer of finished speakers to select the cone, surround, frame, voice-coil, etc. from various sources and have these parts assembled by a finished driver specialist. That's way it's possible to experiment with different configurations without the expense of fabricating the individual (very expensive) parts only to discard them if the results prove unsatisfactory.

That may or may not be how Wilson or any other specific manufacturer orders its custom drivers, only that it's possible. Note how the midrange driver used in the Sasha from Wilson Audio (and in variations in most of that company's newer speakers) at first glance resembles the driver from SEAS shown below. However, if you look closely the resemblance is mainly in the cone material, with significant differences in the dust cap, frame, surround, and presumably the internal structure as well.