If you extend a existing 3 wire dryer/range receptacle,wouldnt you need to bring it up to compliance w/ current code(s) since 250.140 applies to EXISTING installations and if one extends it IMO it would no longer be existing....
Yes it should be brought up to code, too ,many guys afraid to tell the homeowner, it should be code compliant, not wanting to open the walls or spend the money, is not a valid reason, to ignore the code
