Modifier 59 and X Modifiers - Saga to 2018

2014 article on creation of X modifiers
https://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNMattersArticles/Downloads/MM8863.pdf
    and
https://www.cms.gov/Regulations-and-Guidance/Guidance/Transmittals/Downloads/R1422OTN.pdf

2015 article on X modifiers
https://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNMattersArticles/downloads/SE1503.pdf

2018 Update on X modifiers
https://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNMattersArticles/Downloads/SE1418.pdf