My son doesn't always follow all the activities and signs you suggest in each leap. How worried should I be?

A friend of mine downloaded an app that supposedly tells a parent when her son would experience a leap but according to her, it hasn't always been accurate. She looked out for the signs but often found little correlation. She found the entire idea very useful to see what developmental changes to expect, at around what times but most of the time, her son doesn't seem to show the signs and activities at the suggested time. She doesn't seem too worried though. As long as her son is healthy, happy and shows progress everyday, she reckons all is good :) don't worry too much about it!