Loonarloon

I would guess the system automatically does it in a certain time of the year? Since the system is separated drom any government, he didn't need to register himself again or anything, he just "didn't exist" until the system uploaded his revival.

Plus I think it takes into account your achievements throughout your time as a hunter. Since J prolly has the most achievements ever he instantly surpassed even the top dog. Atleast it’s what I think.

I just don't know yet how it knew he was back?

I think it’s like when you log into a game, the game knows you’re online. Or perhaps when you’re away from home but come back, your phone connects back to the internet. I think the system works in a similar way.

No no, what I mean is that he was basically "non-existant/dead", in some sort of chrono-limbo that regurgitated him into the future. the system is not the government, the system came into existance by itself with the rifts. It just "knows" when a hunter exists (as it shows itself when hunters awaken), and even have a classification ranking, so MC coming back into return to "existance" is automatically known by the system, but it wasn't shown until the system uploaded itself. OR I'm completely wrong and the plot didn't think it that deeply, and the system and the ranking are tied to the gov somehow in which case I have no idea how they're gonna justify how he lost his cover.

he has always been the top ranker in the country. i think the system finally realised (or maybe update ?) that he’s still alive and updated the ranking

That's be a fair explanation: it uploads the active hunters so the ranking is not full of dead or retired hunters. However, I cannot understand how having a weapon would impact the rankings as it was implied by the blond hunter. Ranking affected by the possession of a weapon that can be broken or stolen feels weird and something that a human organization would judge, not the system.

This is exactly how I think it is. With how everything was building up from the hunter's mentioning the ranks updating soon and all. if MC came back after the ranks updated, his name wouldn't have shown up until the next rank update

Maybe it accounts to your gear? Similar to mobile games where having even the smallest increase of gear power increases over all power maybe? Like skills, skills levels, and gear probably all is taken into account as well. Of course I’m not sure but it’s probably some combo of a bunch of different things.