I think it's quite excusable to 'notify' if you have the firearm on the seat next to you. That's a bit different, and of course you have to play it by ear being the one stopped. Shame on you for not putting your sticker on your plate. That's part of SA. You failed to have a properly secured and licensed vehicle - it's dangerous to be stopped, so imo, it's quite an epic fail to get pulled for an oversight.
Thanks for sharing the story.