Just google wp8.1 RTM. Man, this isn't opinion, it's a widely known fact. Stop acting like I'm claiming the world is ending or something
Great news! Windows Phone 8.1 has RTM?€™ed after all! | WMPoweruser
With new devices inbound, Windows Phone 8.1 hits RTM status - TechSpot
We RTM our software to manufactures all the time (no, I don't work for MS), and yes, that is the 1st Step when installing it onto the device. However, at NO TIME, that I can remember, has that software ever been the final code base installed & deployed as GA code. Only what the 1st customers in our 'Early Adopter Program' use, and believe me, there are significant bugs in that software, that we follow up with patches as we fix the bugs.
So, technically, yes, its the 'final build' released at that time, and only at that time. By the time its officially released by the phone manufacturers, it will likely have either a respun 'final' RTM or a package of fixes installed on the phone during the official deployment.
We do it every time there's a software release...release to vendors, they find bugs, open up incidents/bug reports we fix and add it to our install package. Its how it works at large software vendors...the install process already looks for a patch package automatically and applies them. The RTM is the final build *SOMETIMES*, but the final product released to end users will be the 'RTM + MS Fixes/Patches + Vendor Firmware + Vendor Software' = GA
Right now we're only at the 'RTM' step...and I'm sorry, but we always can respin a new RTM package within a couple hours if we had enough changes/redesigns that we felt it was necessary. We always have a least a couple of those as well, especially if the patch package is quite large...we'll spin up a new one, notify vendors, and we move forward.
You're getting WAY to hung up on definitions on the internet...and without enough knowledge of how large software corporations actually function.
The only thing true about a 'Final' Package is that there is really no 'Final' Package...