As I browsed the magazines at the store this afternoon, the top line "Sampler Sleuth: Mystery of Missing Letters" caught my attention on the December 2017 issue of Just Cross Stitch. The article discusses omission of letters, dropped stitches, and more. If you are interested in a brief history of samplers, you might wish to pick up an issue while it is still available on newstands. They usually sell remaining issues online.
The article is:
Jennett, Vickie LoPicollo. "Reading Samplers: Not as Easy as A, B, C, 1, 2, 3." Just Cross Stitch 35, no. 7 (December 2017): 42.