All the way until sometime in the mid-1970s, with the exception of (most) post-WW II target stocks. They used to be individually fitted to each gun and numbered so they would match back up after finishing. Exceptions are common.
Thanks very much. I recently picked up a Model 547(9mm) and noticed the number on the grips does not match the serial number for the gun. I don't feel bad, however, since this gun was made in the 1980's after the practice was discontinued. Thanks again for sharing your knowledge.