I have now completely finished this, other than sorting out the two thematic sets of six - which is irrelevant to a degree. …….Sentence removed by Admin ……….
Ten minutes on google/wiki confirmed everything for me - for me, an unknown, and VERY obscure, theme. This proved to be a nice challenge, and my rather fortunate act of serendipity saved a very, very long grid stare - and to be fair, without wiki I would never have finished this.