May be it was planned to be a component of next CU but they found it so critical to wait the official release date.
There are a few people who seem to think that RTM constitutes one big cumulative patch and no solid underlying version anymore. It's an interesting hypothesis and it would be a first. My money is on that not being the case, but only time will tell.
It started with regedit things in WIndows 95 times. We have Windows 10 on 486 CPUs by now. The community found ways to install W11 on unsupported systems. We will see what happens in October...but I bet there will be ways to get W11 on your old computer too (one day)
It happened a few times now, for example 6 months of 19041.1 + patches in the insider channels and at a certain deltabuild (19041.208) it was officially released to the public.
It's exactly what it is, as 19041.1 was also released to manufacturers which used it to image their new devices + installed some CUs on top before selling them (like we all did clean installing it via ISO prior to launch).
Which manufacturers obtained which build? and be specific because I think you are pulling this out of thin air. The only time I'm aware of an OEM receiving a build that needed a CU was the Win8.1 with Update and it was some relatively severe issue where they recompiled the ISO. Both of the ISO files were shared here on MDL in the Win 8 section back in the day. I remember it very specifically because I was doing integrations of the builds at the time. If you have the OEM ISO you're talking about I would love to play around with it in a VM. Perhaps my mind could be changed on this permanent cumulative update RTM situation.
That's what I'm thinking of from the last two comments from P40L0. It gives me the feeling that he comments on things without consistency, which can make people confused. In my opinion, I don't think this can be an RTM version. An RTM version comes more prepared and more consolidated. It is my humble opinion.
That's the whole reason they were stopping to use that useless term. We have seen "released to dev" on MVS (OEM developers not dev channel), next "released to OEMs on MVS and next GA (not a newly compiled build but just a SSU/LCU combo). Microsofoft changed those policies per build the last few major new releases.