You file another claim. Period. It's not unjust enrichment. You have no duty to fix your car. You are being compensated for the reduced value. Say I hit your door backing into a spot and cause a tiny dent. You get paid x for that dent. Then someone comes and rips the door off. The door needs to be replaced anyway. You are legally allowed to put in a claim for that damage. IF someone is to be enriched beyond what they are due, it is never the wrongdoer or the insurer. It is not relevant that you never fixed the small damage.
Now, if you got paid for a small dent on the rear right fender and then you get hit on the door, they only have to pay for the door, not the damage that already existed. In this case you would just list that in the questionnaire about any preexisting marks or dents.
If the car is totaled, you just get book value, so you are out money anyway, because (aside from certain replacement policies) you don't get replacement value only actual value.