It's funny because AWS, at least for the services I knew of when I was there, did rolling deploys to each region over several days. us-east-1 was always the final day because it was the biggest region, so you'd think it'd the safest region since everything getting deployed was well-tested. But while I was there I remember at least 2 COEs where the root cause was basically, "us-east-1 had some hacky legacy configuration that no other region has and that wasn't known/accounted for."