If that is to be dropped, then drop the 3-digit also. If that is to be dropped, then drop the 4-digit also. Only need to change start date. If the industry did not exist the corresponding element points to the industry from which the new industry was carved out. Create a vector of industry start dates.
First step is to create a vector of industry start dates.
Next compare the modified name vector to the original to create a vector of numerical pointers. At this point madefrom contains pointers to parent if exists or self otherwise.