If you got your phone through a network provider. They normally add network optimisation software to updates.
Some networks are faster at sending out updates than others
If the updates are minor, it's possible they won't send it out so.e months and you just get yhe next
Have you tried using Smartswitch and connect to a computer to see if you can get it this way?
If the phone is imported, you may not get all the updates either. Had this before myself
