A story being fixed in time seems to add power to it. Especially when it is a reminiscing about a particular time period.
Temporal setting is as is important as spatial, cultural settings etc.
Extra impact when we get an initial preamble from the “present”, which can set us up with knowledge and expectations during the story (Norwegian Wood, Titanic as random examples).
Foreshadowing in general is a device that contributes to this pattern.
Again, this seems to be a device that increases the sense of fatalism. This was the story of 1969 for these characters. It couldn’t have happened any other way.