I noticed the release date GOG have put in the info is earlier (by one day atleast) and more detailed than the ones found on both mobygames and wikipedia.

The date does seem a little strange being the last day in the year, when the shops are often closed and people are celebrating.

But anyways, is it possible that we could get to know what country/region the release date was for ?

GameFAQs lists the US release date as 12/31/1996. So it's probably the US release date.

The information available out there regarding release dates on this one is a mess and contradictory at times.

In any case, this is the UK version, the US version came a bit later with aditional features (key bindings and difficulty selection), so the release date 31 December 1996 likely is the UK release date.