Images from House of the Dragon hint at how it could be retconning and improving aspects of Game of Thrones' lore. Created by George R.R. Martin and Ryan Condal, the Targaryen-centric spinoff House of the Dragon takes place almost 200 years before the events of Game of Thrones. This is a very different Westeros, one with the House Targaryen dynasty in full swing, dragons soaring in the skies, and the ruin to their legacy done by the Mad King, Aerys II Targaryen, a long way off. Still, that doesn't mean there won't be some connections to Game of Thrones.
While House of the Dragon is its own unique show and aims to be different, it will still have ties to Game of Thrones. That certainly goes on a more macro level - the dragons, the Targaryens, the Iron Throne (which now looks more like the books, a scary, spiky towering seat), and the inclusion of other houses (Lannisters, Baratheons, and eventually Starks will all play their part). Those elements will inevitably color Game of Thrones differently, perhaps especially Daenerys Targaryen's controversial "Mad Queen" ending, which could be better explained (or at least more contextualized) by having so many more Targaryens. It will also be in the smaller details too though: House of the Dragon will no doubt have plenty of Game of Thrones Easter eggs, and one that's already been revealed sets up an interesting retcon.
In one House of the Dragon image, King Viserys Targaryen appears to have the catspaw dagger, the Valyrian steel weapon that was used in the assassination attempt on Bran Stark's life, and later used by Arya to kill the Night King. It's a small but crucial part of Game of Thrones' events, but previously there was no confirmation of who the dagger belonged to in the past; Fire & Blood, the book on which House of the Dragon is based, doesn't specify this dagger as being owned by Viserys (or present in the story at all), but it seems the show is retconning it into the narrative, which is a smart move for providing not only a link to Game of Thrones, but a mirror of it as well.
The House of the Dragon teaser trailer seemingly showed the same catspaw dagger in the possession of Allicent Hightower, Viserys' second wife, who held it aloft running into court looking visibly distressed. In the book, with the rivalry that becomes the Targaryen Civil War known as the Dance of the Dragons in its infancy, one of Allicent's children, Aemond, has their eye stabbed out by Lucerys, son of Allicent's rival and Viserys' daughter, Rhaenyra Targaryen. The events only refer to it as a dagger, but it seems House of the Dragon is retconning it to be the Valyrian steel catspaw dagger. That means there's a clear line to be drawn through the story, with Viserys giving the dagger to his grandson, Lucerys, who then uses it upon Aemond, and it's then taken by Allicent to present to the court the wrongdoings of Rhaenyra's kids.
It's an integral part of the Dance of the Dragons' build-up, and adding the catspaw dagger into it in such a way makes for a natural connection to Game of Thrones, adding to the lore of that show while not taking anything away from this story or feeling forced. Indeed, using the Valyrian steel dagger in House of the Dragon provides a nice mirror to Game of Thrones. Just as here it goes from Viserys to Lucerys to Allicent, by way of great injury to Aemond, in Game of Thrones the dagger goes from Littlefinger to the assassin (or at least, it's strongly implied he hired him, though the books point to Joffrey) to Catelyn, by way of an attempt on Bran's life. Later, it goes from Bran, the boy who will become King, to his sister Arya, a similar passing of the dagger moment in giving it away for an event that will prove monumental.
Even prior to killing the Night King, Arya uses the dagger to murder Littlefinger, showing the dagger's bloody history and the sense of vengeance it carries that House of the Dragon will be adding to. Game of Thrones season 7 setup this retcon, with a similar Valyrian steel dagger appearing in a book Samwell Tarly reads at the Citadel. That suggested the dagger had a much longer history, likely dating back to the days of Aegon the Conqueror himself; House of the Dragon may not confirm that, but it does appear to be making this weapon's journey all the more storied.