The position of the tech manuals and other "non-fiction" works for Trek is... vague.
They've never been declared non-cannon. They were authorized by Paramount. Gene considered them to be part of the background of Trek. The manuals were given to episode writers to use as guides.
Ronald Moore says they aren't canon. Viacom (that owns Paramount) Senior Director Harry Lang said he considers them canon in posts on Trek's official web forums.
That works about as well as a poorly documented, "Gene said at some point." Especially when Gene, being reasonable, occasionally changed his mind on things. It isnt' as if a 50 year old fictional property is going to remain particularly consistent. That a thing is canon and $3.50 will get you a cup of coffee.
Ah, well, that point was not at all clear.
You are talking about a very undeveloped period of franchising (hence the regrettable star fleet battles)
while 'authorised' by paramount it doesn't in anyway make them canon, (see Star Wars novels)
I'm in agreement with Ronald Moore on the earlier books, but the later I books I believe to be canon,
i don't care about the opinion of someone who doesn't know what they are talking about, so Lang is null and void,
Gene's view of Star Trek is canon above reproach, but under developed aspects of canon later get solidified, (like stardate) is hardly surprising, it's unnecessary detail at the time, (they didn't care about it in the 60s) but that changed with time as things became more sophisticated,
btw I remember Gene talking about the 2 nacelles thing in a video, straight from the horses mouth if you will...
And my point was clear within the context of my reply to the person intended,
i would only consider it canon if it was from a source close to the show or printed as such,