[DennisP]

It's not completely nonsensical. The new whisky even from the same distillery won't taste quite the same, due to variations in climate and so on. The old and increasingly rare one isn't trivially replaceable, so if has a reputation of being especially good it can gain value. Even more so when the original distillery isn't in business anymore.

On top of that, the popularity of good whisky has increased a lot over the past few decades, and the higher age statements haven't been able to keep up.