Forget using your intruder system for your fire alarm, its not a recognized method here in the uk.
Buy some proper mains interlinked smoke alarms, they will probably save your life unlike the system wired in alarm cable.
I would indeed question that statement, as its always been required to have calibrated equipment and has been for donkeys. There was a time they wanted regular self-cal as you have said with a yearly cert as well but that went down like a lead balloon and was scraped (still have logs somewhere). But as you may know the NIC make up what ever they want
That's always been the way