We makes train parts. When I first started we were a division of an avionics co., so I know many of the safety requirements are similar and the basic system is nearly identical.
The system is very tight for new builds and this would be impossible. However, for replacement parts, less so if somebody is willing to commit fraud. But such parts are only supposed to come from a certified supplier. If the buyers followed the rules, no way could a fake company get certified.

https://www.breitbart.com/pre-viral/2023/10/05/airplanes-grounded-over-concerns-that-parts-were-sold-with-fake-safety-certificates/ 

 The certification process is vigorous and requires site visits and complete anal exams and periodic audits. This obviously was not done. Following the rules is expensive, faking it is cheep.  If I had to guess, I would guess that they airlines were buying parts on the cheep and overlooking the requirements.  Then something went wrong and are now trying to cover their asses by pointing to a supposed loophole.