The concept of a single barrel Bourbon is easy to grasp. A single barrel is dumped, bottled and when empty another barrel is dumped and so on until the run is finished. So although there may be many bottles each one of them came from a single barrel and not a batch of barrels, or do they?
There's no law that says a distiller cannot dump, say, 20 barrels, mingle the contents, rebarrel the whisky to age again for 3-6 months (Remember Jacob's Well?) and bottle the lot one barrel at a time. This would in fact be single barrel bottlings though certainly not what we think that term means.
What about topping up? Barrels suffer evaporation as they age and there's no law that says a distiller can't take 8 year old whisky still in the barrel, fill up the evaporated space in them with 4 year old whisky, let them mingle for a few months and barrel the lot as single barrel expressions. It may in fact be a better whisky for that with the younger stuff adding a bit of freshness to the older stock.
Under either scenario the finished product can be labeled single barrel. What do you guys think?