One thing worth noting regarding sandpaper and grades/grit, is there is a difference between what we call 240 and what is called 240 elsewhere (mostly US). A lot woodworking & guitar building info is taken and relayed from US based sites so it can be a bit misleading FLOABW.
The differences are small but, again worth taking note of IMO. The different measurement standards are commonly ANSI in the US, and FEPA in AUS/EUR. The aggregate grade is more accurately measured in "microns" which seems to be more universal term. If you look at the attached link below, it breaks it all down.
I mention all this because when I have previously said I have gone to P320 or P400 before staining, I received finger wags of disapproval.
P400 here, is the equivalent of 320 in the US, and P320 here is slightly coarser than 240 in the US.
I think the numbers get bandied about easily without knowledge that one is not necessarily the same as the other.
I've probably explained this in a very convoluted way, but it will make sense when you see the comparison chart.
Again, probably very minor differences in the big picture, but knowledge is power!
sandpaper conversion chart