Consider what you knew about these units and then the implications for Civil War historiography.
Take a look at this passage I wrote just now. Imagine this is a biography:
So-and-so then began what would be a nearly five-year stint in the X Cavalry. Some of the officers in this unit that would later become generals included A, B, and C. Years of tedious garrison duty eventually included some personal milestone (insert marriage, birth, death). With the drawing near of war, the routines of the drill square and the short days would soon pass and X would have to decide on sides in a great struggle as well as find a new role for himself.I think that sums up what's out there in the relevant biographies and why we are so surprised by Puzzle 1 and Puzzle 2.
We have explored (lightly) the Sumner-Johnston-McClellan struggle over cavalry doctrine in the First Cavalry (by way of Matthew Moten's book on the Delafield Commission), but beyond Moten I can't recall a historian digging into these relationships and interactions, 1855-1860.
I could be mistaken but the gaps in ACW history are enormous and they remain year after year. They seem a matter of complete indifference.
Those years McClellan spent as Lincoln's boss on Illinois Central RR legal work - when are we going to read about that? About their many trips to county courthouses on railroad cases? Seems there might be an audience for such writing.
And does anyone care to write that first-ever McDowell biography? It's only been 150+ years, hasn't it?
The idea that Civil War history is actually history often seems questionable.