I don't know how often they upgrade but 1/2 off was too good to pass up. Offroad does not change near as often as urban.
I mapped all of Arkansas from 10,000 feet above mean sea level and that is what the county maps are made from.
That took 10 years.
So I carry a set of 75 counties to cover the state.
I have most of the quads from the USGS of the parts of the state I explore and that is what I have used for years before electronic charts.
I guess I'm a map junkie?