I'm not sure Salisbury's demotion was anything to do with ground grading criteria.
Remember the old "thou shalt not be in administration (or similar insolvency event) on the second Saturday in May or thou shalt be ineligible for entry into the following season's Conference paradise" commandment? Well, that's been extended to cover the whole season. If you're in admin at any point during the season, you'll be kicked out of the Conference system in the summer, even if you settle on a CVA with your creditors. I believe that's why Salisbury weren't eligible for either Conference Premier or South.