Spending Warzone Boosts

I went into the Warzone playlist just a while ago and decided to activate a legendary xp boost for AI kills, I wouldn’t mind not getting any xp if I didn’t kill any AI during the game, but the thing is that I joined the game in progress (something like 600-500) so I didn’t get to kill any AI that spawned because I joined the game so late, meaning I spent a legendary xp boost and didn’t get sh**.
I’m just requesting for 343 to add any way of knowing if we are joining a game in progress or that the boost isn’t activated if we join a game in progress so that we don’t spend such a valuable boost for nothing.