Learn English – Word or phrase for a story that takes place over several years

Saga is sometimes used for long-span, involved narratives. It might connote old northern epics but I've remembered it now in connection with The Forsyte Saga (which tells a story of a large family through several generations in late 19th/early 20th century, London).

Also, looking up this word might bring in more suggestions.

This is another example of a time-sensitive statement, since you would need to update it in a few years.

time-sensitive

2. only relevant or applicable for a short period of time

Most secrets are time-sensitive and cease to be of interest to anyone but historians 20 or 30 years later. Collins

Truths are time-sensitive. They equate to our now. A truth for us today, may not hold as true for us in five years. And the fact that it was a truth five years ago and isn't now, doesn't mean it was any less true then. Into Your Meditation (2016)

You see, God's word is not time-sensitive, meaning the truth of God's word is not affected by deadlines, or the lack thereof. 50 Days of Faith for Entrepreneurs p.55