its what is sometimes referred to as soft- or quasi-canon. as said above, unless it is jibberish or contradicted by something verbally stated, then it is accepted as truth. But this has been the convention even before the age of Blu-Ray. The text in the "Conundrum" bios, for instance. No where is it said that Beverly was born on the moon. But there it is, and is universally accepted. In fact, during the remastering process they are often making the text jibe with accepted canon, often removing the sillier "inside jokes" from the original Okudagrams, like Claire Raymond's descendants being Muppets in "The Neutral Zone"