Nice pair there 'rpm'.....neat...
as for the srial numbers as can be easily seen in the above pictures, the stamping fixture allowed for misalignment, , uneven spacing and in the case of the "10" prefix, different number dies for the 'stamp' itself, look at the "0" different fonts........plus the "bounce"?? shift of the "10" on the upper pictures.....may have come from a different supplier/vendor, stamps (dies) are just that.
the lower serial numbers the "10" is heavy, and the last two digits are a bit heavier...NOT signs of a "reblue".............besides, the lighter ones may have been polished a bit MORE before they were "blued" for the first time....