411 is a fairly up-to-date directory in the USA. Local phone providers keep real-time data for numbers in their service area. For numbers held by other carries, updates are received within 72 hours. Not all carriers share their customer rolls for 411 service, so some numbers are not listed.
The 411 service became decentralized with the break up of the Bell System into regional Bell carriers. As such, the local Bell or AT&T service has real-time 411 information. However, it aggregates data from other carriers every three days. This is also complicated by the fact that other, non-Bell carriers are not required to share their customer lists with 411 and may not be listed at all.