Information got from Victor Martin Guijarro, from National Geographical Institute of Spain (IGN):
From: Martín Guijarro Víctor <REDACTED>
To: Even Rouault <READACTED>
Date: Today 14:24
Hello Even
Finally I confirm you ED50-ETRS89 transformation is under CC BY v4 license. So PROJ are free to transform, modify and distribute it. The only limitation is PROJ or another user must show clearly data are from National Geographical Institute of Spain. This is always compulsory.
https://www.ign.es/web/ign/portal/politica-datos
http://www.ign.es/resources/licencia/Condiciones_licenciaUso_IGN.pdf
https://creativecommons.org/licenses/by/4.0/deed.es_ES
I recommend you this should appear in the metadata files. Examples:
* For a original IGN data: (Data name) (Year) CC-BY 4.0 www.ign.es<http://www.ign.es> - EGM08-REDNAP 2008 CC-BY 4.0 www.ign.es<http://www.ign.es/>
* For a derivated data from IGN data: (Derivated data name from Original IGN Data name) (Year) CC-BY 4.0 www.ign.es<http://www.ign.es/>
Victor
The Spanish grids mentioned at https://lists.osgeo.org/pipermail/proj/2019-December/009082.html are confirmed to by CC BY v4
Information got from Victor Martin Guijarro, from National Geographical Institute of Spain (IGN):