WHAT HAPPENED TO THE 40th & 50th YEARS?

“& thus did the thirty & eighth year pass away & also the thirty & ninth & the forty & first & the forty & second yea even until forty & nine years had passed away & also the fifty & first and the fifty & second yea & even until fifty & nine years had passed away”

Why did Joseph avoid mentioning the ‘decade’ anniversaries? The same thing happens eight verses later, where 70th and 80th are intentionally skipped.

4 Nephi 1:6, The Handwritten Book of Mormon (West Valley City, UT: Dan Wees, September 2017), 642-643.