Case's dating system is real and well documented. Starting in 1970 the company placed ten dots beneath the CASE XX USA stamp and removed one dot each year, so nine dots is 1971, eight is 1972, and one dot is 1979. A different system took over for the 1980s.
Ten dots is 1970. Count the dots and subtract from ten to get the year within that decade: nine dots is 1971, five dots is 1975, one dot is 1979. It is one of the cleanest dating systems any production cutlery company has used.
The dots sit directly beneath the CASE XX USA mark on the tang, visible when the blade is open.
Case has used more than one scheme over its history, and a different marking system covered the 1980s. We are not going to reproduce a full year-by-year decoder here, because only what Case documents itself is reliable and charts circulating online often are not.
The Case Collectors Club and Case's own history pages, linked below, are the sources to work from.
Two visually identical Case knives can be worth very different amounts depending on year, and the stamp is the evidence. It is the first thing to check against any listing claiming an age.
A worn or illegible stamp reduces value because it removes that evidence. See what adds value.