Campground lenghts

Generally you can figure it as being the maximum length for the RV itself, absent a tow vehicle. Generally there will be someplace available to park the tow vehicle separately, though it may not be at your campsite. The best way to know for sure is to call the specific campground (or at least scrutinize pictures of the sites, if those are available).

Sometimes the lengths given are due to access road restrictions, as was mentioned. Sometimes they seem to be assigned at random. Sometimes they're very accurate and precise and admit to no extra leeway.