If you play germany in "Drang nach Osten" than you have many infantery called reserve infantery. I stack some of them together with training officiers but they didn't get upgrade. The germans have no conscript inf, so I was thinking that this is there reserve inf with another name and so I was hoping that they would be upgraded to inf, but that doesn't work. Instead the training officiers grade up inf to elite inf or cav to elite cav but no reserve infantery to infantery which is very hard.