While researching for Falldog's Guide to Gundam Canon and Timelines I was directed to this post by the great Mark Simmons on Mecha Talk back in 2007. In it he references a round table discussion from 2001 in Dengeki Hobby where folks from Sunrise discuss what's canon within the Gundam franchise. The website Mark linked to, at the time containing a transcript of the discussion, no longer exists. However, thanks to the Internet Archive Wayback Machine the content can still be accessed. In additional sections (which I didn't have translated) go on to reference other works and how they view them from a canon prospective. Mark's post on Mecha Talk does a good job summarizing the related content.
For my article on Gundam canon and timelines I went and got the primary section translated by Frog-kun. That translation is provided below for reference.
I asked Frog-kun for details regarding his translation of オフィシャル into canon and this is what he elaborated with,
"I translated the word オフィシャル (which is a Japanese transliteration of the English word "official") as "canon" a few times mainly to avoid repeating the same word over and over. If you don't think it fits, you can replace it with "official". From what I understood of the conversation, though, it did feel as if they were discussing official versus non-official continuity in a way that was very reminiscent of discussions about "canon" in the English fandom sense. I used the word because it would help put the discussion into perspective for an English reader.
"Also, you're right that Japanese fan lingo doesn't have a word like "canon", but there are words in everyday use like 本編 and 原作, which mean "original work". Discussions about what constitutes "official" work are still matters of contentious debate, and many Japanese fans hold the original work at a higher level of esteem than any subsequent adaptations.
"So yes, there was a bit of interpretation going on when I translated オフィシャル as "canon", but at the same time, I don't think the concept is absent in Japanese fandoms. "