Open Question: Does cobra coverage start date pay for any health insurance claims after my insurance termination date?

basically resigned from job became self employed continued health insurance through cobra coverage but before i officially had cobra coverage i used health insurance two days after my termination date of my health insurance ...after using health insurance i found out it had terminated two days before but the cobra coverage start date continues from the termination date of my health insurance. the claim was on the 22nd termination date was the 20th but now my cobra coverage continues from the 21st so i have a 1200 dollar bill that insurance didnt cover does cobra coverage look from the 21st on and cover any claims i had ...i didnt have insurance at the time but now i have cobra coverage that continues from the termination date so does cobra go back and cover that date?