Back in the 90s I assembled a binder of all the (not yet) legacy encodings then in use sourcing from ECMA and elsewhere. It was four inches thick double-sided. Unicode had just seen its initial release and it wasn't clear if that would be the universal text encoding or if it would be ISO-10646 which attempted to maintain a semblance of backwards compatibility with the morass of non-Latin/extended Latin text encodings then in use. There were five commonly used encodings covering different sets of Chinese characters alone (Japan, Korea, mainland China, Hong Kong and Taiwan all had their own encodings and selections of characters). Kids today with their UTF-8/16/32 don't know how good they have it.
Isn't the Unicode codepoint repertoire pretty much identical to ISO 10646? AIUI Unicode only differs by standardizing additional character properties and rulesets, but the encodings are supposed to be identical.
They weren't using Unicode at all.
Instead they were using 'prehistoric' fonts patched by changing the glyphs in ASCII fonts(100s of them). This too without proper conventions.
They way to convert these to Unicode is by creating character maps in a font-by-font fashion.
ISO 10646 does not work as you describe. I'm pretty sure most of the character encodings defined by creating a custom font were never standardized by ISO.
