Apple has now stopped signing iOS 12.1.4 firmware recently after the release of iOS 12.2 with many more new features.
That is you are no longer able to downgrade or restore your iPhone or iPad to that firmware version from iOS 12.2.
So you have no chance to downgrade back to lower version anymore. If you want to restore your device from iTunes or OTA, then you will force to install Apple’s current latest firmware iOS 12.2.
And those who have accidentally updated your device to iOS 12..2 via OTA or iTunes, downgrading back to iOS previous versions like iOS 12.1.4 or lower is not possible.
Apple always gives older versions of iOS to restore whenever it releases a new version so that people can have the ability to downgrade their devices to the previous version if they are not satisfied with the new one or any issues. But after some time, it stops signing the previous version and allows the latest iOS version only.
You can also visit this link https://ipsw.me to check the signing status of Apple firmware.
Also, there are lots of users that are going to be affected by this change, specially Jailbreakers. The Jailbreak hackers usually work on to build a jailbreak on older versions and have now successfully jailbroken on iOS 12 using Unc0ver.
So Jailbreak lovers who are on iOS 12, 12.0.1, 12.1.1 or 12.1.2, do not update to the iOS 12.1.4 But if you do not care about Jailbreak, you can upgrade to iOS 12.2 anytime.