I have noted the variation of thumb pieces on N and K Frame guns, but for the first time, I paid attention to the ones on some of my little guys... I have exactly six Chiefs Specials in my collection... with variations in thumb pieces:
SN 26261:
SN 46042:
SN 315974:
SN J88217:
SN 89J740:
SN BEK1510:
1st photo is 1st style flat latch (2nd type thumb piece used on Chiefs)
2nd photo is 2nd style flat latch
3rd photo is 3rd style flat latch
4th & 5th photos is 4th style standard thumb piece (the 1st thumb piece used on Chiefs until ~ #111, and final style used on all I and J frames after 1966).
6th photo I wouldn't call a different style, just a manufacturing/finishing variation.