The build number for iOS 12.4.4 is 16G140. Apple has mentioned in their release notes, about a FaceTime bug which they fixed in iOS 12.4.4 which may have lead to arbitrary code execution.
Apple may have been trying to patch the checkra1n Jailbreak exploit for these older devices by these software updates. They may have tried to patch the Jailbreak exploit in the earlier versions of iOS 12, like iOS 12.4.2 and iOS 12.4.3. For those who are unaware of the checkra1n Jailbreak, it is a Jailbreak which is enabled through a hardware bootrom exploit known as checkm8 by axi0mX. This is a hardware exploit, which most probably, cannot be fixed by a software update. This will allow jailbreak developers to create an exploit for any software version. The devices from the 4s to the iPhone X. Apple had also released an update for the iPhone 4s and the iPhone 5 which were iOS 9,3,6 and iOS 10.3.4 respectively in which they may have tried to fix the bootrom exploit.
To stay secure, it is highly recommended to update your older devices to iOS 12.4.4 unless you would think of Jailbreaking your iPhone.