I have seen なら used when drawing out a conclusion based on other person’s actions. (飲むなら乗るな) But I wonder if it can be used in a following fashion: if iťs the case that I… I must have… (as if one is trying to remember whether they did something) Also, can “we” work too depending on context? If so, could you please provide any simple example sentences?
Yes, it is possible.
- アメリカに行くならビジネスクラスで行きたい If I were to go to the US, I would like to take a buisiness class.
- 私が母にプレゼントするならこちらを選びます If I were to give my mother one of these, I'd choose this one.
I guess this may help (on why you thought なら cannot be used in the case you have in mind).