Different O days- is it possible?

Christine
I'm sorry if this is a dumb question but, is it possible to Abe different ovulation days. Like last cycle is was like cycle day 21 and I'm pretty sure I ovulated on cycle day 16 this time around... Could that be?! That's what CM was telling me (I was a champ at OPKs last cycle and this cycle took them like maybe once a day which is also why I think I already peaked.) Any help is appreciated. Glow tells me my 31% day is today buuut, CM is back to sticky and lighter color on OPK