The Earth is dynamic. Differences may be due to the age of the published values and/or the methods used to establish them. Due to much of Louisiana being prone to subsidence, for example, a position in a subsidence zone may have changed by an unknown amount over a 25-year period, and the published values could be stale versus what you measure today. Published values may have been established with legacy methods or reference frameworks that do not have the same network accuracy as more recent ones. Plus, the marks may have been set 25, 50 or 60 years ago, and there may be many reasons why they might be suspect. We suggest doing check shots on recently published NGS or LADOTD marks with NAD83-2011 values. You may wish to use a “localization” or “calibration” (it is called different things in different vendors' field software) routine if you need to constrain your project to old, published values.