To add to Erin’s comment, it was never said that all of D1 is now folklore. This is what Margaret Stohl, a Narrative Director at Bungie, originally said:
grimoire is considered folklore, even to the inhabitants of the universe: true as far as they & we know!
She later clarified what she meant:
Let me reassure you - we all agree destiny’s lore is one of the great gifts of the universe & we don’t ever want it to go away - if anything, we want to explore more & more of it in the future - huge apologies if my tweet last month (below) threw you off - not my intention!
Christopher Barrett also provided clarification as to what she meant, as Erin has mentioned. It was never said that the grimoire was going to be retconned, or that it is no longer canon. There have been numerous references in D2 to the grimoire in D1 which shows that it is still considered to be part of the lore. For example, the quest for Saint-14’s shotgun in Curse of Osiris, which involves your guardian going to Mercury to find out what happened to Saint-14, ties in with the Legend: Saint-14 card, which showed that Saint-14 travelled to Mercury years ago in search of Osiris.
That said, I do not agree that all of the grimoire is folklore, although some of it can be considered to be folklore. Nor is it all from a biased or unreliable perspective, although, again, some of it is.There are many cards that include recorded conversations, letters, and messages to people. The content of these conversations etc may be false or biased but they are still accurate records of what was said. Of course, this assumes that these records have not been tampered with or altered. A few text logs, such as Ghost Fragment: Thorn 3 may have been altered considering that Dredgen Yor’s original name is not mentioned but instead shows up as [REDACTED]. However, the vast majority of text logs etc, such as the recorded conversations in the ghost fragment cards for the crucible maps, do not show any signs of tampering or alteration. Recorded conversations, letters etc are generally taken to be an accurate record of what was said, so why would the writers include these cards in that format if they’re not actually accurate after all? And if they aren’t meant to be taken as being accurate, then why have the writers not included a clear explanation on why they’re not accurate? For example, if the Vanguard or the Consensus has a history of altering records to suit their purposes, then this could explain why records may have been altered, but aside from the redaction of Dredgen Yor’s original name in the text logs there hasn’t been any hints that the Vanguard or the Consensus regularly alters records.
The cards on the enemies, places, weapons, etc, such as The Fallen and Earth cards, also do not fall under the category of folklore. These cards are written to sound like encyclopedia entries that provide factual info. The purpose of these cards is to provide a brief, concise summary about, say, a particular character or enemy to people who are new to the world of Destiny or who don’t know much, if anything, about a particular topic. For example, if a player has just met Ikora and they want to know more about her, they could look up the Warlock Vanguard card. Considering that these cards are meant to provide basic information about the world of Destiny to players, why would the writers include information in them that is not accurate and true? It would be very confusing, particularly for players who are new to the game, if they read, say, the Goblin card and it said that goblins are one of the Hive rather than the Vex.
It’s also worth mentioning that even cards which could be considered to be folklore, since they are from a biased and/or unreliable perspective, still include information that is known to be canonically true. For example, the Books of Sorrow are told from the perspective of Oryx, his sisters, the Worm Gods, and others, so it is likely that parts of it are biased or exaggerated. However, it still includes information that has been confirmed elsewhere to be true. For example, we know that Oryx had a son called Crota and two daughters named Ir Anûk and Ir Halak. We also know that Oryx had a massive ship called the Dreadnaught and that this ship has a very powerful weapon, as described in XLI: Dreadnaught, which was used to attack the Awoken forces in The Taken King. The numerous references to Savathun in D2 also make it highly likely that Savathun does actually exist, and that she is one of the Hive, although at this point it hasn’t been confirmed outside the Books of Sorrow if she is Oryx’s sister or not.