Useful Blogs with interesting QSL info:
Arild’s DX Diary: https://dxblog.wordpress.com/
Hugo’s DX Hoekje: https://hugosdxhoekje.wordpress.com/
Maresme DX: https://maresmedx.blogspot.com/
MolaDX: https://moladx.blogspot.com/
Peter’s DX Corner: https://petersdxcorner.nl/
Info via WOR via DX fanzine