Yes. Let me explain how we send out an OS upgrade build.
Lets take the example of a device on S which we will upgrade to T OTA.
First a S build will be released which will be mandatory for the users to install.
Next only those with this S build will be able to see the T upgrade build when it is released
For FP4 we will release a v1.20 /e/OS S build 
- this is the part that is delayed and awaiting confirmation as to when it can be released.
User who install this v1.20 /e/OS S build will get to see the /e/OS T build when it will show up as part of v1.21
I am waiting for a confirmation from the team when they can release the v1.20 /e/OS S build for the FP4