I use to have also older bottles of blended scotch (JW red label, VAT69, White Horse, Black & White, etc.) in my cabinet, all earlier then 1980, as they contain different malts AND a higher ratio of malts (which again differs from the ones you can buy today) then today and taste excellent. That's why they seem to "age"...the destillery shake out in the early 80ies resulted in "adjusting" the blends as some of the malts were not available anymore.
Why same single malt with different age taste different - I don't know.
I think Laphroaig needed to change the process in the mid 90ies. Just compare 10y with 43% from the 90ies with the currrent 10y 40% bottling - much different.
But I have no glue why Talisker 10y from the 90ies tastes much fuller bodied and simply better then the current bottling.