They do use a family table on the fly, just like assembly cuts, and the information is stored in the referencing assembly. The dimensions of an assembly cut can be driven by relations and parameters, but not the dimensions of flexible items.
My basic rant on flexibility is that it should be only defined at the sub-assy/part level. The person making the original knows the items that can reasonably be altered at installation. I swear someone somewhere has decided to make a screw a different length using the flexible modifier and production can't figure out why the screw doesn't fit, even though it is clearly shown as fitting in the assembly and the part verifies as matching its own description.
Flexibility should be bottom-up and have dimensional limits available to ensure that only reasonable parts can be generated.
They also need to add a curvature controlled sketch element, both geometry generating and reference, so that flexible variations can be made of items that are conventionally flexible, like living hinges. Wouldn't it be nice to have an item that can deform from a CW bend to be straight to a CCW bend based on a single value?
