I'm honestly not trying to be difficult. I am trying to understand how you can use the 5.1 SRD to produce legally protected works for other editions of D&D, and what the limits are. I get that a derivative work can re-define elements in the SRD to "revert" them to their 3.5 definition. What I am confused about is how you could add things explicitly not in the 5.1 SRD but in another edition. Can you, for example, make a 4E retroclone? If so, could you release THAT into CC?
I know I don't have an exact answer for your question, but something that I recalled while reading it may be of use to you, and if you know all of what I'm about to write, then apologies again.
In 2015, Necromancer Games released a monster book called "Fifth Edition Foes". This was a year before the 5.1 SRD was released under the OGL 1.0a.
They were using Open Game Content previously released and cited the 3E SRD for their rule references. Due to the mechanical similarities between 3E and 5E it worked pretty well.
If you look it up, you'll note stat blocks are laid out just a little bit differently, information is slightly shifted from where you'd expect to find it from the official 5.0 stat blocks. And they used modified phrases like "tactical advantage" to refer to the Advantage mechanic, but of course this wasn't explicitly stated, just inferred. There was an expectation that you the reader were already experienced with 5E and would know what this meant.
I bought the book at the time it was released and used it to great effect. It provided my campaign with a lot of unique and unexpected monsters that didn't appear in the 5.0 monster manual.
I will say, I don't know if the book was ever updated after the release of the 5.1 SRD, but that release version provides an example of how compatible content might be produced without an edition specific SRD.