Bilbo was declared dead while he was away in the Hobbit (and had to do a bunch of paperwork to get declared alive again) but there’s no indication he was formally declared dead after leaving the Shire, even though most people assumed he had died.
Therefore I posit: having a missing person declared dead in the Shire requires the consent of their next of kin. Whoever Bilbo’s next of kin was at the time of the Hobbit (possibly Otho? I’m not sure) had him declared dead at the first opportunity but Frodo refused to ever do it.
Frodo had anxious hobbit bureaucrats knocking on his door every couple of years like ‘Mr Baggins… blease… it’s been 10 years… he was eleventy-one… can we fill out his death certificate yet’ and Frodo was like ‘absolutely not’.
Early on he genuinely couldn’t bring himself too but after a while it was more that he enjoyed irritating the local magistrate’s office than anything else.
I raise you: the hobbitish bureaucracy has no means to re-declare someone dead. They had no precedent to declare someone who was once-dead dead again. They would need the Thain, the Mayor, and the Master of Buckland to agree to changing the statute, and since the Thain and the Master are too amused by the whole henclucking that they haven’t gotten round to it just yet.
I’m upping the stakes with: last time Bilbo was declared dead when he was, in fact, not dead, they removed the law stating that you can have someone declared dead without a body, so when Bilbo left (happily aware of this legal loophole and snickering) he could never become legally dead again.
I am loving the implication here that Bilbo can literally never die in the eyes of the law. He’d love that.
a hobbit parent telling their kids the story of Mad Baggins and being like “thanks to a loophole in hobbit law he’s technically still alive today”
a hobbit child misinterprets this and lies awake at night worrying that Mad Baggins is still out there and will appear in their room without warning