In most of the US …
After a person dies, the body must be turned over to either the county coroner or a licensed funeral company. Either of those entities will type up the information on a “request for death cert” form which is turned into the county department of births & deaths. After several days to a couple of weeks, the county will prepare an original official death certificate & certify it. Somewhere along the way a licensed MD, often the patient’s GP, will determine & certify the cause of death.
After that, interested parties such as next of kin can obtain “certified duplicates” of the death certificate from the county. After paying a fee and waiting a few days for the bureaucracy & the snail-mail.
Knowing the process, most funeral companies will offfer to order & receive a few copies on behalf of the next of kin as part of their normal services. For an additional fee of course.
So the punch line is that, at least in the USA, there is period of up to 30 days where the person is 100% deceased, but the legal paperwork hasn’t caught up yet, and there is no way to *prove * in the full-up legal sense of the word, that the person is deceased.
You will find that every agency & corporate department which routinely deals with the aftermath of a death is used to this delay. So, for example, you can call SSA or the deceased’s life insurance company or whatever & tell them what’s happened. They’ll take your word for it, but won’t take any irrevocable action, like paying out the life ins, until they get the certified copy.
I’ve also noticed that very few things, other than life insurance, insist on no kidding original certified duplicate DCs as sold by the county. A plain old fax of a certified original is good enough to close utlity accounts, get refunds on car insurance premiums, that sort of thing.
Nothing, other than the need to refrigerate the body, happens in a hurry once somebody stops breathing. A month’s delay for a piece of paper is trivial in the whole post-death administrative process.