How does Cirium source data?

For general information about how we collect data see here:
https://www.cirium.com/who-we-are/our-data-science/ 

Cirium ingests data from a number of sources which have developed from years of building trusted relationships. Primary sources include airlines, aircraft registers, OEMs, banks and lessors; with additional information obtained from clients, airports, operators, regulators, news providers, social media and photographic evidence.

Cirium’s data researchers and analysts check and validate information against multiples sources which are recorded, tracked and audited.

More reading.  How Cirium sources World Fleet data can be found here: 

https://helpdesk.cirium.com/hc/en-us/articles/360024623551-What-data-sources-are-used-to-track-the-world-s-fleet-