Bret Devereaux

It was a major issue during all the wars where we used volunteer regiments. Written improperly, the 15th NY could be NJ or NC or NV. Stating the "15th Regiment" could be just about anyone. It organized everything to a far greater extent

I understand the basic admin headache... But do we have actual examples where it caused significant problems? Orders issued to wrong unit in a battle or campaign, or pay not getting to a unit, etc?

It wasn't only that. The USV system was a horrible mess, relying on state governments to do more work than they really could. It also erased the issues between USV officers and Regular officers, about primacy of rank. Federal funding went to NG units to bring them to the...

Sure. But did numbering have to follow that? It's not like we're the only country in the world that had different numbering schemes and eventually standardized training and ranks. Others... didnt seem to find renumbering necessary...

You understand that the regimental numbering system, both state and federal, were always in flux until 1916, correct? They changed. A lot. Within states. By war. And we're by no means the only Army to do it. Look at France and England. England's erased half their old regiments

The Romans numbered legions by consular sequence (so each consul/pro-magistrate might start at I and have legions II, III and so on). When those became permanent formations, the system was kept such that there were 2 IIIs, 2 IVs at one point *four* Legio IIs...

Only under the Empire. The Republic would reassign numbers, raising & disbanding legions in a regular basis. Thus Julius Caesar’s favored Legio X had little association with the Legiones X of the Empire.

Caesar's Legio X is the Imperial Leg. X Gemina, sometimes called Leg. X Equestris after the famous bit with the horses in Gaul. It has a bull as its emblem to explicitly advertise Caesarian origin (he was a Taurus).