You have a point. We will never know. To me, to see a full clean 50BTC reward from first era it is a rarity. Aside from Satoshi, how many original full 50BTC are there? The information is not useless. If there are many, it means we are still to early and that at any point more 50btc rewards will come to be sold. If there aren't many, then it means that the first era is finished and we move to a next step.