If D&D Beyond is considered an official source, how do you figure which part is official when parts of the site contradict other parts?
Example: the monster page for the gelatinous cube says:
Senses Blindsight 60 ft., Passive Perception 8
While the gelatinous cube's entry under Monster Stat Blocks in the Basic Rules says:
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 8
(All monsters have mundane vision, without any range limit, by default, unless that parenthetical note is there, so one version of the cube can see someone 65 feet away with normal sight, while the other is naturally blind and can't.)
If a monster is naturally blind, it has a parenthetical note to this effect, indicating that the radius of its blindsight defines the maximum range of its perception.
Another example: the monster page for shadow says:
Skills Stealth +4
But its entry in the Basic Rules says:
Skills Stealth +4 (+6 in dim light or darkness)
(One DDB user did point out this discrepancy in the shadow's Stealth skill on the site already, in a comment on July 7, 2019; although that comment is wrong about Undead Nature, which is correctly omitted since it isn't part of the statblock.)