From: Utlima Thule
anything in the reserve, under NM and not on 'rest' will train automatically, basically it will reach the NM and then stop. Gds get a bonus so not only do those units have higher potential moral, they end up with higher experience.
I tend to look for low exp formation and give them obsolete planes, so any trainig losses are not on the most modern stuff.
there is a some chance of more exp > NM but it slows down.
Now this is an endless process to be honest, you simply have to chuck 50 exp formations into action, watch them get ripped apart and repeat the cycle.
My advice is that before late 43 at any time you should have at least 40% of the VVS in the reserve, that enables you to sustain the allocate to map/die/retrain cycle and keep your front line airforce intact.
Over time (& esp once you get Gds formations) this cycle slows down, slowly you get formations with above average experience from combat wins, at the same time the LW weakens (both in numbers & competence)
If you disband an airgroup, the pilots go into the pool but are treated as 'trained' so picked up by TPI formations. If you train to 50, this can be an effective way to keep your TPI formations relatively strong and over time above average (don't do this with many formations though).
if you disband when an airgroup first appears (ie it has low exp pilots), they too are treated as 'trained' and used for TPI, even if they are at 30 exp. So don't disband till the air group has decent exp - but careful disbanding can get your on map pilot cadre to improve a bit more quickly