This is a good point.
The world moves on, people move on, party support evolves. In the 80s, lots of people who had voted Labour decided to vote for the Alliance or the Tories- what was in their bones was less clear, and didn't matter anyway. Labour adapted andn a load of new people started supporting Labour, and some elections were won, and some were lost. That's the way it goes.
The SNP have picked up a lot of support in the last decade or so. Do the more longstanding supporters play the "bones" card on the newer ones? I doubt it very much, apart from the tiny number who've joined Alba. This is the political equivalent of "I was there when we played Welling away on a Tuesday night", isn't it?