Japanese fandoms as a whole don’t put nearly as much emphasis on canon as Westerners do, so it’s not always so cut and dry. As far as the FSN manga is concerned, it’s an adaptation of the primary work with relatively little input from the original author, so obviously anything that contradicts FSN proper you can safely ignore, and anything manga-exclusive that doesn’t explicitly contradict anything else exists in a state of “maybe it’ll show up again if one of TM’s main writers saw it and liked it.”