Mikasa Tattoo and she having a bandage that covers it is nothing new. In fact we seen the Bandage since Chapter 5. Chapter 5 of the Manga is when during the Trost Arc the Collosal Titan penetrates the 2nd wall (wall rose) at the location of Trost but not the 2nd penetration of the other side of Trost for the warriors were trying to lure out the Founding Titan.

During Chapter 5 Mikasa gets angry at a merchant prioritizing stuff / food over human people and Mikasa gets angry. A mother and daughter are grateful to Mikasa's intervention with the Merchant. This gratefulness then starts a flashback in Chapter 5 of how Mikasa was told to hide the mark from her mother.

What I am saying this information is not really new information it is just a combination of being so long ago (literally told 8 years ago in real world time) combined with it not seeming salient at that time and thus it "snuck up on people" including myself



Later on in the next chapter (#6) we continue the flashback of Mikasa's past and we see Mikasa and Eren meeting due to the death of Mikasa's parents followed by Eren trying to save Mikasa and also Mikasa triggering her Ackerman blood.

---------

Now the anime is a separate thing from the Manga. It seems the tattoo / clan symbol was cut from the anime but most of the events I detailed occur in episode 6 of the anime. Perhaps the clan symbol is shown in a different episode but I do not see it in episode 6 with a quick reviewing (note I was skipping around instead of watching all 20 minutes of episode.)

---------

Now the Iceburst stone has been mentioned a couple times before but often it is not the stone that is mentioned but the gas that the stone produces. The most prominent mention that connects the Iceburst stone to the Gas the 3D Maneuvering Gear is in the Attack on Titan Guidebook. There may be other references in some of the spin off works such as the attack on titan prequel comic (Attack on Titan: Before the Fall.) That said the importance of Iceburst Stone was barely hinted at before, but this is the nature of the Attack on Titan Manga. For example the Thunder Spear Tech is a modified form of the Anti-Personnel Vertical Maneuvering Equipment meant to fight humans and not titans, and the Anti-Personnel Vertical Maneuvering Equipment is in turn a modified 3DMG. Us learning that the stones is important not just the gas is a another similar (but not the same) progression as what I just described.