Cryptic pregnancy

I know there are cases where some women have undetectable pregnancies until 20 weeks or some even until birth because of low hcg levels and other factors. I recently read on a page called cryptic pregnancy support group that because the hcg levels are so low, pregnancy lasts much longer from 40 weeks to 9 years. That sounds absolutely insane????? Is that even possible or is that made up? I looked up that the longest recorded pregnancy was 375 days, so a little longer than a year. Just curious if this is true because I absolutely could not imagine thinking you’re pregnant for 2 years but not being able to detect it at all,,, sounds absurd.