Answer: MapInfo Pro uses the \p#### or Projected Coordinate System (PCS) codes shown in the example when registering GeoTIFF images or other georeferenced raster images. GeoTIFF files often identify their coordinate system with a single code number instead of listing the coordinate system parameters, so MapInfo Pro scans the MAPINFOW.PRJ file to find a matching supported code. MapInfo Pro supports a subset of PCS codes, depending on the projection they use, in values between 20000 and 32760). Codes cannot be used more than once in the MAPINFOW.PRJ file.
Example:
"- Australian Map Grid (AGD 66) -"
"AMG Zone 47 (AGD 66)", 8, 12, 7, 99, 0, 0.9996, 500000, 10000000
"AMG Zone 48 (AGD 66)\p20248", 8, 12, 7, 105, 0, 0.9996, 500000, 10000000