QGIS (current 3.4.4 version) have almost all its CRS definitions as EPSG Authority codes.
But many of them are not registered in the https://www.epsg-registry.org/ database, so many of them really have not an EPSG Authority.
By the side, at this moment that lack of support is causing QGIS not recognizing the CRS of the layers exported to non-EPSG authority codes, as can be seen in the following posts:
- Several projection issues QGIS 3.4.3
- CRS information not recognized when geopackage is loaded
I'm trying to understand the QGIS CRS codes (sr_id and auth_name fields of the tbl_srs table, in srs.db) database, and how QGIS writes and reads the CRS of the layers and try to match them with its database.
And what I can not find is the reason: Why almost all the codes in the QGIS database carry the EPSG Authority when really many of them are not in the EPSG registry?