There is no real way to sort these aberrations out, but in most cases they can be identified as 'suspicious' if that matters to someone. And of course there is always the potential for the 'screwdriver variations' arising from easily-swapped parts that muddy the gun's actual date of origin, either 'early' or 'late'. There will always be the occasional 'late shipped' gun having bits and pieces that were released considerably after the gun's serial number might indicate, or the occasional gun wearing some older bits from way earlier production that just floated to the top of the 'parts bin' at final assembly. He can, for instance, occasionally come pretty close to revealing within a month's time when certain features/parts were changed in a run of a particular model. His serial number breakouts are considerably more precise than anything Ruger has put out, and his discussion of which parts were used when is further informative.
Knowing the month as well as the year certainly helps since the various 'type' configurations of many of the Old Models are pretty well known and documented in Chet15's Red Eagle News Exchange Reference of Ruger Firearms.
