Osprey isn't actually too accurate much of the time. A lot of Osprey can be stylized or simply wrong sometimes, so we only use it as a source if none others can be found. We've been able to make some very good units though, with plenty of primary and reliable secondary sources to base things from. Osprey is a last resort, and Roman accounts aren't always all too accurate either (like 'lazy Gauls' in Carthaginian armies, despite their statements, right beforehand, how hard the Gauls were working for the Carthaginians). We can usually (but not always),find better sources, archaeological as well as textual, for the units and armies.