I believe when OP said 'treated this as a late validation error', they were acknowledging the inevitability of bugs and root cause-ing "why did a single failure

I believe when OP said 'treated this as a late validation error', they were acknowledging the inevitability of bugs and root cause-ing "why did a single failure to validate cause the entire system to fall over rather than reject the single flight plan in question." The words 'treated this as' are load bearing here.