Is Iron Will applied retroactively?

Iron Will is a perk purchased from the Officer Training skill, which does the following:

Soldiers received a larger Will bonus each time they are promoted.

This is very useful, but most of my squad is already fully promoted, so if it's not applied retroactively I'm not sure if it's worth it.

Is Iron Will applied retroactively?

Solution 1:

No, it is not.

Your already promoted soldiers will be at a will disadvantage to the new soldiers you receive. If you record the will levels of your existing soldiers and then take the upgrade, you'll see that it doesn't change.

Because of this, its better off if you get this earlier in your game rather than later.