The version history of the methodology library or manual showing the planner's name against the revisions over several years, supported by the training records showing the planner taught it to others.
Authorship is proved by revision history, not by a letter saying so
An employer letter asserting that an employee developed a methodology carries limited weight on its own. Contemporaneous internal evidence is stronger. For a Torbay mining-services company that keeps its failure-mode library in a document-management or version-control system, an export of the revision history listing dates, authors and change descriptions is strong evidence because it was created for operational reasons. Supplement it with the training curriculum showing the planner as instructor, sign-off sheets or learning-management records for planners trained, project reports where the planner's thresholds were applied and their results, and any internal certification the company grants on the methodology. If the company does not have a version-controlled system, dated email threads, meeting minutes and signed-off procedure revisions can serve the same purpose. Present the material with a short index so that an officer can find the planner's name without reading hundreds of pages.
Hypothetical example: a Torbay fluid-power manufacturer keeps no formal version-control system, but its engineering team retained dated design-review minutes, access logs and training sign-offs. Those contemporaneous records can establish authorship when organized in a short chronology. A first review should ask who created each item, when, and for what operational purpose. That provenance matters because a newly written support letter merely repeats a claim; the dated project record is what lets a reviewer test it.