And even still today this kind of manual hand-patching will be done for minor bug fixes (instead of 'recompiling' the layout from the RTL code). One motivator

And even still today this kind of manual hand-patching will be done for minor bug fixes (instead of 'recompiling' the layout from the RTL code). One motivator is if the fixes are simple enough, the modifications can be done such they only affect the top-most metal layer, so there is no need to remanufacture the masks for other layers, saving time and $$$.