There is a distinction between “as found” drawings (drawings that depict the reality of an existing building as it is “found” today) and drawings that were “found” in a search to locate historical documentation about a building. This is not to knock the value of original drawings that are sometimes available when working on an historic structure. Its just a reminder that original drawings do not always provide accurate descriptions of what was built. Depending on when and how the building was constructed, design drawings sometimes were more like polite suggestions.
The other issue with “found” drawings is how they are converted into CAD drawings or BIM models. Care must be taken to avoid a messy foundation for preservation work.