dialogs are the corresponding EPSG code for the projection.
These are used by GIS software packages to when converting files to different GIS formats, to define a common standard coordinate system different software can understand.
For example, when MapInfo exports a geopackage file or a ArcGIS Shape PRJ file. The MapInfo coordinate system is converted based on its EPSG code.
Custom or local affine coordinate systems are no supported by the EPSG database. Archaic projection systems also do not usually exist in the EPSG database.
