Post-truth of inscriptions - dilemma of wall painting conservation

Inscriptions are important element of many wall paintings. They are not only part of interior’ decoration but also written document of history of the building. After many years every work of art can be damaged or changed by overpainting and needs conservation and restoration. The fundamental question is if the rules of reintegration of lost parts are the same for all paintings or there is a system specific only for inscriptions?
Examples from conservator’s practice show, that there is no strict regulation for protection of “documents written on the wall”. Damaged historic inscriptions are often completed and even reconstructed.