It's been law ever since I've had a certificate and that's some years! What has happened in the past two years or so is that there's been a tightening up on the law, with police, BASC, GTA and others all singing from the same hymn sheet and this because so many RFDs and FAC holders were bending the rules (don't shoot the messenger!) and not complying with the law. It is neither confusing nor nonsensical, but is really quite simple. If you buy a firearm then the law clearly states that the SELLER must enter the details directly onto YOUR FAC, (read your FAC...it is stated on there) hence mail order or not, your FAC must be presented to the seller who in turn completes the details and you get it back. No problem with doing this by post because in the extremely unlikely event your cert goes missing, it is reported to your FEO and a duplicate issued. The more sensible will use Special Delivery which is warranted post, so there is no need for any dramas. I've bought and sold firearms this way multiple times.