Yeah it seems there are 2 coordinate systems, one “internal” which we see in mission descriptions(e: and companion info) and which uses contiguous coordinates, and one “external” which is used on overmap itself and increments not at 999 but instead at 200-something or whatever. I don’t remember exact number.
I noticed the difference between the mission coords and overmap coords a while back, its definitely a bug of sorts, but idk how to fix it, not really an area I know well.