User blog comment:LilyheartsLightning/Citadel and Reckoning DLC announced/@comment-737801-20130221183242/@comment-1440333-20130222031409

But Collector Swarms are mentioned in the codex under The Reaper War. Plus it is a little foolish to assume ALL the collectors were destroyed on that base - there were trillions of Protheans, and as they were not turned into Reapers it stands to reason a great percentage were harvested as Collectors.