Hi,
I wanted to provide a brief assessment as to why, in my opinion, there were so few issues in the tests on Staging (see Enabling Asynchronous Order Finalization - #5 by aarongable - ""This has been (quietly) enabled continuously in Staging for a week now. We have not seen any increase in errors, nor have we received any complaints or bug reports from clients issuing against Staging.""), but there were so many errors during the live rollout.
The reason is probably that such breaking changes mainly cause problems for old clients - and old clients are usually running on older systems and quietly doing their job against the LE Live system. There are probably very few older clients running against Staging, why would they ... mainly this happens when implementing new LE clients on new systems, etc.
Just a little food for thought! 
Best regards
Andy