There doesn't seem to be a ISO 8859-12. Any pointers to information on this topic would be hugely appreciated.

ISO 8859-11 <-- ISO 8859-12 --> ISO 8859-13

I find some old references which say it is going to be for Celtic languages, but ISO 8859-14 does Celtic and these same source say that -14 is going to be for Sami.

Were it to exist, it would presumably share the first 160 characters with ISO 8859-1 or Latin-1, as do all members of the ISO 8859 Character Set family.

Research continues...