I'm supposed to have one a year (cancerous cells in the past) but hadn't had one since I moved house over 2 years ago . Then I finally got round to having one and it was insufficient . THEN I had to wait another 2 months to repeat it as it takes a while for the cells to grow back apparently, and that one was normal (phew!) - just got the result a few days ago.
I will have them every year from now on, anything could happen in 3-5 years, especially as the results are not 100% reliable (more accurate these days with the new method of taking cells but still not perfect). I went from always having had normal results to suddenly needing a large part of my cervix removed!