@esoteric_programmer Basically, instead of constructing an iso9660 format image and index once and wirting that, most early CD writing software used a form of packet writing with UDF (Universal DIsk Format), through sessions left open, so you could keep appending new data without having to rewrite the entire thing.

It was common enough that the resulting volume would present a small iso9660 volume with the UDF support drivers and software so it could be read on earlier systems.