AFAIU SDXL is actually an erm genetic descendant of SD1.5, with its architecture expanded, weights transferred from 1.5, and then trained on bigger inputs (512x512 in the end is awfully small). SD2.0 is a completely new model, trained from scratch and as far as I'm aware noone's actually using it. Also noone is using the SDXL refiner if you go to civitai it's all models with detailer capabilities baked in, what you do see is workflows that generate an image, add some noise at the very end and repeat the last couple of steps. Using the base sdxl refiner on the output of other sdxl models is sometimes right-out comical because it sometimes has no idea what it's looking at and then produced exquisitely surface texture details of the wrong material. Say a silk keyboard because it doesn't realise that it's supposed to be ABS and, well, black silk exists.