Just got back from GC. Our experience at Mather was that there were MANY sites that were not occupied, even though they said it was full. I think the NPS only opens a set number at a time for reservation. I would ask at the campground office (not the gate) and see what they say.
The village was VERY crowded when we were there in mid-September. Its like being in a foreign country, English was by far the least heard language. ( the US is on sale right now for Europeans due to the exchange rate). This was certainly not a problem, just surprising.
A better alternative for us was the Desert View NPS campground, deserted, quiet and isolated. It may close at the end of October though. We had a great time there. Be advised there is no dump station at Desert View, closest is at Mather.
Burns & Diane
2005 Winnebago Aspect 26A/2012 Subaru Impreza toad
Illinois! - Where the politicians make the license plates......