Haha! I'm glad you got this all sorted out!
There are slight differences between batches, which is easier to notice over a prolonged time period, not just two bottles on a shelf. Some distilleries embrace it, and don't necessarily try to exactly imitate prior offerings, instead turn to numbering the batches and creating some marketing within the expression (Aberlour A'Bunadh, for example). However, most expressions within a brand are remarkably consistent over time.
Another issue that came up is how long the bottle had been open. Like it or not, alcohol evaporates, and when it does, the whisky mellows out and changes the profile of the dram. I have seen this on a number of occasions where a bottle was opened and nursed on for years.