This is just one of several loosely related questions... A while back, what started as a "simple" investigation of the rabbit hole has (inevitably) turned into another full on open-pit free-fall of learning the hell out of it and exploration for me. It's times like these I question myself and wonder how much I really need to know to effectively benefit from my inquisitiveness. I'll avoid backstories and unrelated tangents for now to spare everyone's time and get down to brass tacks.
I'm (always) still learning and humbly welcome corrections to anything I may be misrepresenting, have an incorrect understanding of, or any usage of improper terminology. I'm not looking to root, modify, unlock, or any other shenanigans just yet because I feel it's important to understand and practice the fundamentals first. So for now, I'm trying to get a solid grasp on flashing pure vanilla, keeping everything as stock-OEM as possible
I have several XT926s and I've noticed that on the ones that have the final update/build the About phone under Settings shows a Build number of "KDA20.64-15", which is also displayed in the recovery. Some of these units have booting/boot-loop issues or other "quirks" once booted. My understanding at this point is that these problems can essentially be attributed to either a hardware failure or software corruption. Assuming corrupted software, the consensus is to flash the device with the exact same firmware version or updated version.
To get to the point, I've been trying to find the KDA20.64-15 FXZ, but I've only found KDA20.64-15.1 which I've successfully flashed and verified on at least one device. I'm trying to understand what the difference is between these two versions, if any at all. I'm sure I'm wrong on this, but my initial guess was that this was a way to perhaps differentiate between how the phone received the firmware; for example, KDA20.64-15 is "official" via OTA update or installed at the Moto factory/authorized OEM warranty repair center, and KDA20.64-15.1 is a leak or public/developer version. The most relevant information my searches turned up are in the links below:
(self explanatory and not that helpful)
(more applicable, though it doesn't seem to address my question)
(the most insightful and useful, but not quite to my satisfaction)