I was more than sure that each subsequent flights causes to overwrite earlier FDR and CVR recordings. How then should I understand the following part (emphasis mine) from this Wikipedia article:
The National Transportation Safety Board downloaded data from the aircraft's recorder and found it was a habit: 98% of the previous 175 takeoffs were made with incomplete flight-control checks. The National Business Aviation Association analyzed 143,756 flights in 2013-2015 by 379 business aircraft and only partial flight-control checks were done before 15.6% of the takeoffs and no checks at all on 2.03% of the flights.
Is it truly possible that single FDR unit kept 175 past flight's data? Is it possible that NBAA was able to retrieve approx. 379 earlier flights' data from 379 planes (143,756 / 379 ~= 379), spanning even two years into the past?
What am I missing here? How long data is kept and not overwritten in single FDR unit?