Those are the ones you hear about. Then tgere's the ECI level Snowden leaks on US companies "SIGINT enabling" their products. It said the FBI "compelled" those that resisted. SIGINT enabling is backdoors. The method of compelling isnt revealed. And Lavabit case was similarly expected ti keep secret of it all.

So, you are told that it happens as you describe. We cant be assured of tgat given leaks.