It was never a hard cutoff, nor was it universal. Technology has long been a big factor, which means people in rural/poor areas were a decade+ later in experiencing the same generational norms.

Even cultural cornerstones are variable. For instance, you might remember the Challenger, or you might not, depending on your early childhood schools and your memory. The news about Magic Johnson or Kurt Cobain may have shattered your worldview, or you may not have even noticed.

But even in the best case, these are only useful as a rough guide. You should not be trying to do anything specific with these generalizations.