I don't know where did he pulled that info from.
There are no federal regulations about over-subscription ratios, and carriers are not required to report data on the performance of their networks to anyone.
You're correct - oversubscription ratios on class 5 switch (line to trunk) are up to 5:1 for business, and up to 9:1 for residential lines. That ratio can be dynamically adjusted depending on the load at the moment.
There are FCC regulations regarding emergency (911) calls, and that service has a number of high availability requirements.