Can we have a longer luteal phase ?

Subhashini
I have read that LP won't vary beyond one or two days and usually it will be between 12-16 days. Than if someone ovulated say on 15th of some months , she should get AF by 1st or 3rd or max by 5th of next month , but what is causing delayed AFs ? The regular answer I saw is counting ovulation dates wrong but what if we calculated the ovulation date correctly?