Ok, option 3 suffers badly from the poor definition of Steadfast in the BRB, so it can be interpreted in 2 different ways. Therefore, it really should be divided into 3a and 3b. Let’s try this again, with a summary of arguments for (+) and against (-) each interpretation. Did I miss something?
1. Detachments may count the ranks of their parent unit for the purpose of steadfast. This does not require the parent to be in combat at all.
2. Parents that are steadfast gives steadfast to their detachments that are involved in the same combat.
3a. Parents that are steadfast gives steadfast to their detachments, even if they are not involved in the same combat. The parent gains Stubborn in the first place by outranking the enemy it is fighting, and it may then pass it on to its detachment. Whether the parent wins or loses its combat is irrelevant.
3b. Parents that are steadfast gives steadfast to their detachments, even if they are not involved in the same combat. The parent gains Stubborn in the first place by fighting its enemy before the detachment does, losing the round of combat, outrank its enemy, pass its break test and it may then pass it on to its detachment.
Option 1
+Pretty elegant rules design.
+/-It is no doubt the most powerful interpretation, and may be considered overpowered. Or not.
-Wierd situation: A parent standing in a river or similar can’t be Steadfast themselves, but would still allow the detachment to be Steadfast on the parent’s merits. Option 1 would need a clausul saying that the Parent cannot pass on ranks if it is in a situation where it can’t be Steadfast itself.
-Wierd situation. 3 rank Parent fights 10 rank enemy, while 1 rank Detachment fights 2 rank enemy. The Parent is not steadfast itself, but still lets the Detachment count its ranks to obtain Steadfast. Similar to the situation above.
-This is simply not RAW. The new Detachment rules only states that parent units share Steadfast with their detachments. Having many ranks means nothing with regards to Steadfast if the parent is not in combat. This interpretation would need a serious errata, not a FAQ.
Option 2
+Elegant rules design. Doesn’t create any wierd situations. Both Parent and Detachment are in the same combat, and so win it or lose it (and take break tests) together, the same instant.
+/- Clearly the least powerful interpretation.
-Not quite RAW. The new Detachments rules don’t mention being in the same combat as a prerequisite for sharing Steadfast.
Option 3a
+Most RAW, as long as you accept the definition of Steadfast in the first place.
-Wierd situation: 3 rank Parent fights 2 rank enemy, while 1 rank Detachment fights a different 10 rank enemy. The Detachment is Steadfast although clearly it should not be.
-Wierd situation: A parent in a building is Steadfast (not Stubborn, oddly enough) and passes it on to its detachments outside. The issue lies more in the Building rules than in the Detachment rules, but it is still there.
-Suffers from the “sequencing” problem; the order in which you resolve combats becomes important, as the parent’s Steadfast status may change (due to loss of ranks, losing and breaking, winning and breaking the enemy(!) etc) before it is time for the Detachment to fight.
Option 3b
+Most RAW, as long as you accept the definition of Steadfast in the first place. However:
-This definition of Steadfast cannot be correct. If you “gain” Steadfast the moment you make your break test, it stands to reason that you “lose” Steadfast the moment you resolved the roll. If Steadfast status only exists at the moment you make your break test, the detachment cannot get Steadfast from it’s parent since they don’t fight at the same time (given that they are in different combats of course, but if they are not, we have reached option 2, above and it’s no longer a problem).