Somewhere Right Now In The Future is the first one that comes to mind. It's the one that sounds most like if could be pulled directly from the Old Tunes era, yet it's not impossible to imagine someone cooking it up as "New BOC found omg"
Incidentally, I almost might not have clocked Naraka as Boards of Canada if someone told me it was BOC and I had 0 Inferno experience or other context. That's not a knock against it at all, I like it and it is definitely BOC, but it's not something I expected!
Introit I would have also believed to be "too on the nose to be real" if it was released on soulseek 8 years ago as a 128kbps mp3. But I've been duped by some very bad fakes in the past so who am I to judge.
Into The Magic Land feels like the one that I would have clocked the BoC influence but got you couldn't have convinced me was them. I would 100% have got excited about hearing it though if it had leaked because I'd have been convinced there was an interesting band that was taking lessons from them and going somewhere completely different.
For the one that I had no doubt was BoC it's hard not to say Prophecy. I know when I heard it for real we knew it was them, but my first thought was "this sounds nothing like what they've done before but it's so obviously them". If I'd heard it in any other context, if they'd uploaded it under a false name, I'd be starting the conspiracy theory it was them
Their production is pretty unmistakable. I think perhaps Somewhere Right Now in the Future would be the most dubious because it's more lofi, but still, those chord progressions are distinctly BoC. I would probably be most confused over Acts of Magic at first now that I think about it.
i guess i interpreted the question as though if an individual track were leaked ahead of the release, how would i react to each track individually in the even that each was a singular leak (e.g. 'if someone leaked The Process on may 10th would you have thought real or fake')