Trap - I've seen many original finish Kodiaks with the blond color... become real dark when re-finished. Would guess the same would happen to your 62" 59 KS if it were refinished.
I call the black material on the belly at the tips, Underlays, as a means to differentiate from overlay material. Just trying to make a common language more easily understood.
Not sure there is a chronological order to the underlays. Never really tried to figure them out as to me they are simply one of many cosmetic features that are not worthy of consideration for dating bows.
I would not be surprised to learn that there are exceptions to high-low 1959 serial numbers with or without underlays.
I would think in a few days, that we could get a few dozen 1959 Kodiak Serial numbers of various lengths to see if a pattern emerges with or without underlays.
Of the 9 I've shown on this thread, 3 have underlays. Of your two, 1 has underlays. BowDoc has two, that is 13. If we can get a couple dozen more, we may see a pattern.