...(i came across someone with some overdumped 901120 disks) no idea how they managed that, but it does happen.
OK, I haven't spread them, I just deleted them when this happened, but I have used software (on the Amiga) that over time creates disk images this size. It's been about a year since I've actually even been on my A2000, so I can't remember the name of the software, but I was creating ADFs from FMS virtual drives (pretty sure it was FMS...it's been a while!)
I would un-DMS to the FMS device and then copy the corresponding image (renamed as an adf). Most of the time this would work, but at some point, the filesize changed, I would have to reboot, delete the fms images, and create them new all over again. This should at least shed some light on how these images happen.