Nice stamp though there have been cases where the Golden Toad, Tasmanian Tiger/Thylacine and Caspian Tiger are probably still around but in small numbers.
There have been cases where animals thought to be extinct have been rediscovered, also it's estimated that there's over 8.8 million plant and animal species alive today but only a quarter have been discovered.
The closest thing to a Quagga I've seen are Zonkeys(Zebra/Donkey) and Zorses(Zebra/Horses).
It's virtually impossible to prove that something doesn't exist. However, at least in the case of the thylacine, it's existence is highly unlikely. It has been searched again and again for more than 70 years without a single good piece of evidence. Not that I don't want to believe they're still there, but mostly it's just wishful thinking.
You have a point, though many researchers have found tracks and made footprint cases.
Plus there are areas of Tasmania that have been unexplored since the 1920s and the government at one point still had it listed as endangered and I doubt all the reports of people seeing them are wrong.
On the other hand, all the large scale expeditions to find proof of thylacines have failed. I hope you are right and there is enough unexplored thylacine habitat where a small population might still persist.
I have read the eyewitness reports, and some of them do seem credible enough to believe in. Unfortunately though, human observation is incredibly unreliable. Where I live, it happens once in a while that moose hunters shoot each other and afterward claim that they clearly saw a moose, with horns and all, coming through the bushes instead of a man in bright red clothes.
It is, fortunately, pretty common for species to be rediscovered, since it's next to impossible to really confirm an extinction. Rainforest amphibians, pygmy primates and shrews are rediscovered all the time. However, rediscovery of a large carnivore that has been gone for more than 70 years, despite being extensively searched? Very, very rare. Not impossible, but unlikely.
Can you direct me to the source of the howling wolves in Honshu? It sure sounds interesting. Though only the voice is not too convincing: dogs howl too. Honshu is also really, really densely populated and has been that for a very long time. It's unlikely that a population of large carnivores would have avoided contact with humans in such a place for a hundred years.
To compare: in Finland, there are 16 people per square kilometer, in Japan, 337 (and Honshu is the most densely populated of the islands). Still, our 150 wolves seem to collide with humans all the time despite there being so few of them they are probably going extinct in a few decades due to inbreeding. Even I have seen wild wolves once.
Of course, the mountain ranges in Japan give some additional shelter to wildlife.
I wouldn't be surprised if it turned out there is some Honshu wolf blood in Japanese dog breeds. Wolves were, apparently, tamed multiple times in other parts of the world and the dogs derived from them then interbred with each other and, once in a while, with the wolves of their region. In the far north, sled dogs are still mixed with wolves once in a while. So why not in Japan too?
A nice story. I do like to think that the Tasmanians could have just domesticated their thylacines instead of paying people for killing them. Though they did also kill the native people, so why expect humanity towards animals?