It gets murky I think.
Way back in the '70s between TOS and TMP a lot of fans deferred to material in print to "fill in the gaps" of TOS' backstory and history. For a long time (and for some of us still) the details James Blish had in his adaptation of "Balance Of Terror" were accepted as fact in terms of what happened during the Earth/Romulan War. Stuff found in Franz Joseph's blueprints and technical manual, as well as other publications, were accepted as gospel even though any potential future productions were certainly not beholden to them. So it's not surprising that some fans deferred to backstory details Gene Roddenberry put in his novelization of TMP as effectively canon even if none of it appeared in the film itself.
To that end it's not all that surprising the producers of STC just might defer to the TMP novelization given it was written by Roddenberry himself and thus giving it a measure of authenticity no other published work might have.
That's how it was for me. You had the Blish and Foster serializations, the books written by Gerrold and others, the Technical Manual, a slow drip-drip of Trek fan and professionally written fiction, occasional Trek magazine articles and the Official Star Trek Trivia Quiz.
All we knew were in these pages.
It's akin to the book of mormon vs the bible.Agreed and as a fan film series, it's pretty high up.
But...
That is totally real from a lot of fans and extremely ridiculous. It's not nearly on that level.
) the details James Blish had in his adaptation of "Balance Of Terror" were accepted as fact in terms of what happened during the Earth/Romulan War. Stuff found in Franz Joseph's blueprints and technical manual, as well as other publications, were accepted as gospel even though any potential future productions were certainly not beholden to them. So it's not surprising that some fans deferred to backstory details Gene Roddenberry put in his novelization of TMP as effectively canon even if none of it appeared in the film itself.