Maybe a point is deducted for lateness, or you can no longer get 100 after 2 tries, or some stipulation to show accountability and timeliness, but this is totally valid. Redoing it shows that they care to get it right!
My son's Language Arts teacher allowed them to resubmit written assignments for a potential higher grade after editing and making corrections-- that's how writing works! Few things are once and done. The most highly esteemed writers have editors, and submit many, many rounds of rewrites; why should kids be expected to get it right on the first try?