Getting the latest update can be a bit trick on some Android devices. There are devices known where the "Check of updates" does not every time really check for updates, on such devices hammering the "Check of updates" button 10-20 times can help. I don't know if this also applies for Nokia 3.1.
Another "update blocker" is if your device is branded by a Mobile Network Operator (MNO). In such a case the MNO also has to release the update which can take weeks to months. Therefore IMHO buying a MNO branded device is a bad idea.
Third online updates are never rolled out to each and every device at the same time. Consider a new release that requires the download of ~300 MB that is released for 1 million devices. If all devices would start download at the same time or within a short time frame this would cause a denial-of-service attack against the download server. Therefore updates are usually released step-by-step to the devices. If your device belongs to an "early" or a "later" update group is invisible to the user.
If Nokia provides a PC based update software you may be able to update your device using it. Such a PC based update mechanism is usually not restricted to certain devices as it is not widely used.