i dont think it really matters, they are always wrong anyway. I wish i could be that wrong at my job all the time. I have wondered what the difference is though. The way i see it is that you got a 50% chance of rain every day, its either going to rain or its not!
Scattered would be something on the order of 20%-30% of the area/region gets wet from several thunder cells. Isolated would be something on the ordr of less than 10% of the area/region gets wet from a few very widely dispersed thunder cells.
Partly cloudy vs. partly sunny....Most people get this one confused as well. Partly cloudy can be worded to mean the same thing simply by saying "Mostly" sunny it just depends on what affact the broadcaster is after.
Most of us who spend a lot of time outside can predict the weather much more accurately than the NWS with a minimal understanding of conditions and a simple radar loop.