Here is how it was discussed over on our "local" board. A synopsis of everything Fidelis has been saying since the beginning.
Cut and Paste....
Let's start with the relevant rules:
"If a Regimental Unit has any of the special rules listed below, they confer the same special rule onto all of their Detachments whilst they have at least one model within 3": Frenzy, Hatred, Hold the Line!, Immune to Psychology, Stubborn, Steadfast, Stupidity." (WA:E, p.30)
"If a defeated unit has more ranks than its enemy, it takes its Break test on its unmodified Leadership." (BRB, p.54)
So, moving on to the scenarios:
1. Detachment in combat/Regiment unengaged.
-> The Regiment is unengaged, not in combat, etc. For starters, only defeated units gain Steadfast; victorious units are never Steadfast. According to the two rules above, a unit has to be in combat and has to have lost to be able to benefit from Steadfast. Since the Regiment is not in combat and hasn't lost, it's not Steadfast.
2. Detachment and Regiment involved in two seperate combats.
-> Steadfast is not a continuous effect. A regimental unit will never give its detachments Steadfast if they are in two different combats because it only ever is granted at a moment in time, and combats do not happen simultaneously.
The only scenario in which a Detachment will benefit from Steadfast from its Regimental unit is when they are both in the same combat. Say the Regiment has 5 ranks, the Detachment has 2 ranks, and the enemy has 3 ranks. In other armies, the unit with 5 ranks would be Steadfast and the unit with 2 ranks would not. However, the Regimental Units rules override this, allowing the Detachment to benefit from the Regiment's Steadfastness...provided they are within 3".
I'm sure it won't matter but I thought I'd give it one more whack.
Noght