Medical evaluators must understand the context for the impairment assessments they perform. This article exemplifies issues that arise based on the role of impairment ratings and what edition of the AMA Guides to the Impairment of Permanent Impairment (AMA Guides) is used. This discussion also raises interesting legal questions related to retroactivity, applicability of prior precedent, and delegation. On June 20, 2017, the Supreme Court of Pennsylvania handed down its decision, Protz v. WCAB (Derry Area Sch. Dist.), which disallows use of the “most recent edition” of the AMA Guides when determining partial disability entitlement under the Pennsylvania Workers’ Compensation Act. An attempted solution was passed by the Pennsylvania General Assembly and was signed into law Act 111 on October 24, 2018. Although it affirms that the AMA Guides, Sixth Edition, must be used for impairment ratings, the law reduces the threshold for total disability benefits from 50% to 35% impairment. This legislative adjustment benefited injured workers but sparked additional litigation about whether, when, and how the adjustment should be applied (excerpts from the laws and decisions discussed by the authors are included at the end of the article). In using impairment as a threshold for permanent disability benefits, evaluators must distinguish between impairment and disability and determine an appropriate threshold; they also must be aware of the compensation and adjudication process and of the jurisdictions in which they practice.