Back around 2013, some folks found some leftover samples in a South African lab, after everyone felt that all samples were disposed of. I would make a guess that you can find hundreds of labs around the world that have samples packed away. Some aren’t aware of it...some probably have rogue scientists who just kept it for a private project.
I would suggest this...if any episode occurs and it leads back to North Korea...there probably will be a level of destruction laid down that would make the images of Berlin in 1945 look minor in detail. Even the Chinese have to be looking at this suggestion and be fairly worried about the nutcase in charge.
Even the Chinese realize germs do not respect borders.
I’ve read that people in the arctic who died of smallpox and were buried, decades later, upon re-examining their graves live smallpox virus was found. Same for flu of 1918.