Legendary and WB's Monarch Sciences website is beginning to share more information regarding Godzilla: King of the Monsters as well as tease more monsters joining the burgeoning MonsterVerse. It wasn't long after Gareth Edwards' Godzilla reboot released in 2014 that WB decided to fully develop a shared universe surrounding some of the most famous kaiju/monsters in film history - and that's what ultimately led to Jordan Vogt-Roberts' Kong: Skull Island, which released in 2017.
Aside from the organization Monarch having a presence in Kong: Skull Island, the 2017 film mostly existed apart from the Godzilla movie. However, thanks to the introduction of the hollow earth points and Kong: Skull Island's post-credits scene, Godzilla: King of the Monsters is able to introduce a handful of new monsters - specifically Mothra, Rodan, and Ghidorah - into the MonsterVerse in unique ways. And much of that has been teased on the Monarch Sciences website. But the viral site may also be subtly bringing old Toho movies into canon (or, at least their events.)
After debuting the first Godzilla: King of the Monsters trailer at San Diego Comic-Con 2018, the Monarch Sciences website (and Twitter account) went silent. Finally, months later, they're back with new teases on Twitter, some of which were revealed during a Godzilla panel at LA Comic Con in October. What's interesting about these new teases, however, is that they could be perceived as subtle references to past Toho movies, and are thus potentially evidence of WB bringing old Godzilla events into canon.
For instance, Monarch's tweet Godzilla heading to the last known location of a Japanese land mass that sunk into the ocean is referencing the movie Submersion of Japan (aka Tidal Waves in the United States), a disaster movie about a series of geological phenomena leading to Japan sinking. Then, Monarch's tweet about Godzilla disappearing and then reappearing in the Sea of Okhotsk is certainly a nod to the 1991 movie, Godzilla vs King Ghidorah, which makes reference to a time Godzilla defeated King Ghidorah in the Sea of Okhotsk, where King Ghidorah had remained for 200 years.
Considering that WB is only now getting back on track with using Monarch Sciences to promote Godzilla: King of the Monsters, there may be plenty of more opportunities for them to reference and tease old Toho movies, while also possibly bringing them closer to the events of the MonsterVerse. Of course, they don't need to explain how everything could potentially exist in the same universe, but it's not like having a multiverse is too far-fetched.