A variety of errata for spells and items are published on D&D Beyond.
The question What is the rarity of an Amulet of the Shield Guardian?, for example, notes that D&D Beyond contains a reference for a master's amulet needed to control a shield guardian that is otherwise not listed in printed resources.
As I understand it, D&D Beyond is an official publication of Wizards of the Coast. If D&D Beyond rules are official for Adventurers League this would clarify rulings for spells and also clarify that the rarity of a shield guardian's amulet is rare (it's otherwise unstated).
Are D&D Beyond spells and items official for Adventurers League?
Best Answer
Maybe.
The AL Player's Guide and AL DMG don't address which rules to use outside of setting minimums and outlining the "+1 rule." So we turn to the AL FAQ (version 7.1 as of this writing) which contains this relevant guidance on p.2:
So it has to be "the official rules," and PHB, DMG, MM are examples of such rules.
The next page makes a bit of an argument against, in that it lists twenty-four separate sources and doesn't list D&D Beyond, but arguments from omission are inherently weak, in my opinion.
That said, since the differences between D&D Beyond and the PHB, for instance, haven't been issued as errata you're "safe" going with the legacy wording.
Proceed with clarity.
In a few months we should be seeing a set of AL documents in the v.8 form which one hopes will make some mention of D&D Beyond. Until then just be clear with your players/GMs what you're using. Either "I don't see D&D Beyond the list so I'll stick with listed sources" or "it's an official WotC product which is what they say to use" certainly strike me as legitimate positions. As usual: what is important here is probably not so much arriving at a "correct" conclusion as is arriving at a shared conclusion.