Hey, cut me some slack I was typing at the same time you were. Will do on the email...And yeah its another long night, its late fall ,rainy season, Im a seasonal defective, and Im trapped on midnights..and this and research are my only relief, so Im going mad,AND IM TAKING YOU WITH ME ..BUHWAHHAHAHAHAAAAAA
Hello renovate7 :
As 03man so shamelessly expressed the info is in the new 99 book. It appears that the first use of the serrated safety was at serial number 78499, off and on, then completely by 89997 till 99952 . So basically one can say that the last 10,000 rifles of the 6th series used the serrated safety feature.
Changes in parts usage in the Japanese rifle production tend to start and go back to previous parts usage till the old design is used up and then the new one takes its place, this is not an instantaneous change but may happen over the span of thousands of parts later. Then you have where in the back shelf you find a box of early parts and those are used till gone, so it is possible to find earlier and later parts used with no concern over what future collectors might think of that !.
If the parts are numbered and are correct make otherwise it maybe original even though it is out of sequence according to our studies, that is what makes collecting 99s so interesting.