Here’s an important notice from The National Geodetic Survey (NGS) concerning the new GEOID12 model:
The National Geodetic Survey has determined that the GEOID12 model was developed using erroneous input control points, primarily in the Gulf Coast region. NGS immediately corrected these errors and developed a replacement model: GEOID12A. GEOID12A is now available for public analysis and comment on the NGS Beta website for GEOID12A and will soon be released for production.
Localized errors were found in parts of Louisiana, Mississippi, Texas, Alabama, Oklahoma, and Canada. Errors in Enid, Oklahoma, and Canada were identified shortly after the August 8, 2012 error notice was posted. After receiving critical input from surveyors, the control data used to develop GEOID12 were immediately re-evaluated, and problematic control stations were identified. Once the problem control stations were corrected, a new model, GEOID12A, was developed. The differences between GEOID12A and GEOID12 are displayed in the map, below. (Click on the map to open a full-size PDF version.) The map shows all areas where GEOID12A differs from GEOID12; in all other areas, the two models are identical (except for the localized errors in Canada).