Often small populations of a species that has been officially declared to be extinct, but which is actually just functionally/ ecologically extinct, continue to linger on for decades in the wild. Typically this persistance might just be a handful of individuals and they may go unnoticed due to difficulties of conservationists conducting fieldwork in more accessible areas.
For example , I have read that there is some fairly substantial and notable evidence that some thylacines may have survived in the more remote regions of Tasmania right up until the 50's and 60's. However, the odds that there are any thylacine still existing in the wild today are beyond negligible and despite all of the "sightings" that occur every year the chances that these are genuine are highly unlikely.
There is typically a much higher incidence and likelihood of smaller "lazarus species" being rediscovered such as small mammals , birds, amphibians , reptiles and insects than large mammals. These kind of things are sort of normal and the rediscovery of species originally recorded by some intrepid Victorian naturalist but that have "disappeared" for over a century literally happen every year.
I think its more probable , particularly in consideration of the levels of poaching and deforestation in Laos and the fact that these antlers were found almost 30 years ago, that the Schomburgk's Deer is extinct. But interesting article and fingers crossed that there are some still out there.
