Don't understand the real meaning of (only new users in the past 90 days)

From my understanding, if I choose users who did some event within n days. There should be only recent 90 days data because it said that (only new users in the past 90 days) . But actually when I choose user who did an event within 10 days. The earliest data is about 100 days ago. When I choose user who did an event within 50 days. The earliest data is about 140 days ago(chart link here).  I don’t think this is corresponding with what you said about (only new users in the past 90 days). So I’m wondering if anyone can tell me the real meaning of (only new users in the past 90 days).