here's 1 I saw for guard..
Q. Are you required to spend a doctrine point to
be able to take Storm Troopers and then an
additional doctrine point for Grenadiers?
A. No just the one, Storm Troopers are Imperial
troops assigned to a regiment in the field.
Grenadiers are elite members of the same
regiment.
So, what if you wanted a stormtrooper army, using 3 elite stormtrooper units and 3 units of grenadiers... then you have to use 2 doctrines? or still just 1?