Outside the RPD, there's a restaurant called "Mikhail's Pierogies", a reference to Mikhail Viktor.
Mr. X's new fedora is based on an early piece of concept art, where he was depicted wearing a hat.
In the lobby of RPD during a 2nd Run, the player can check security camera footage on a computer. They then see Mr. X walking on the screen, and smashing the camera. This references the encounter with him within the Umbrella lab from the first game.
During HUNK's bonus mode, the 4th Survivor, when Nighthawk says that time's up, he ends up saying to him "This is war; survival is your responsibility." when the latter refuses to leave the Reaper behind. This is a call-back and inversion to The Umbrella Chronicles: in the bonus level of the same name, HUNK coldly abandons one of his surviving team members who radios him pleading for help by saying the exact same thing.
Of course Leon would be retconned into wearing a jacket at the beginning of the game. He has been wearing a jacket before switching to something else in every single ResidentEvilworkinvolvinghim.
The "Welcome Leon" banner in the West Office has a noticeable gap between the L and the C, and an extra L can be seen sitting on a desk underneath. This is poking gentle fun at the original's "Wellcome Leon" sign, and implies that someone caught the error after the banner went up and quietly fixed it.
The Umbrella lab branch under Raccoon City is called the NEST, a clear nod to the Hive from the live action films.
In a 2nd Run, you can access the stairway under the entrance to the RPD which can't be reached on the first run. The room you find there includes a recruitment poster with Brad Vickers on it, alluding to the Easter Egg in the original where he appears as a zombie if you reach that same location without picking up any items along the way.
Wesker's desk still has a film reel with a picture of Rebecca in an RPD basketball uniform on it. You just don't have to check for it 50 times this time.
The Dark Room has the old S.T.A.R.S. team photo from the older games in it, complete with the unknown bald guy with a mortar in front of him.
Leon's 2nd Run exclusive Colt 1911 aiming stance is the old "gangsta lean" aiming stance from one of his costumes in the original game, while Claire still fans the hammer of her Ruger Blackhawk like she did the SAA in the original.
Every once in a while, the player will come across female zombies wearing red tanktops and brownish-green shorts that look an awful lot like this one◊ right here.
HUNK's position at the beginning of The Fourth Survivor is Point K12 down in the sewers, which is a callback to Goblin 6's distress call from The Umbrella Chronicles.
In Leon's scenario, the door to the shed containing the Club Key will start rattling violently when approached, and getting even closer will cause two zombies to burst out from the room behind it. This is a nod to a specific door in the original game where, if opened, zombies will appear and attack the player during the loading screen. Said zombies are even replicated one-to-one in the remake, right down to them wearing similar clothes.
Whenever Chief Irons spots Sherry in her stealth section, he will says "I see you" similar to Jack Baker.
Expendable combat knives are a nod to the self-defense Daggers of the remake of the first game, though changed so that killing the enemy the knife was used on lets the player retrieve it if it's not broken, whereas you could only retrieve them in the former if you destroyed the enemy's head quick enough after using them.
Mr. X's death scene when Leon finishes him off is remarkably similar to what happens to another T-003 in Resident Evil: Damnation, complete with a darkly humorous "gotcha" moment as the smoke clears. It also invokes the end of Mr. Baker's boss fight in Resident Evil 7.
Claire's route to the orphanage is a remix of the original path to the Raccoon Police Department taken during the original game's A Scenarios, while Leon's route to the sewers only cuts through the Kendo Gun Shop.
Claire's JMB Hp3 has a laser sight on it, replacing the normal aiming reticle and giving her an aiming system more like Resident Evil 4's. Leon's Lightning Hawk's sight upgrade gives him a similar red dot on his reticle, but doesn't take away the crosshairs on the screen.
Next to a typewriter in the NEST you can see the same Birkin family picture that Sherry carries with her in the original game.
The Ivy Zombies in this game are a clear homage to the "Green Zombies" or "Plant Zombies" of Resident Evil Outbreak, being human corpses visually parasitized by T-virus-infected plant life.
Pale Heads, which are described in a note found at the beginning of Runaway as a rare mutation of zombies, are clearly evoking the Crimson Heads from the remake of Resident Evil 1. Their appearance invokes the "naked zombie" skin from the first and second game, which is absent in the core game of the 2019 remake. Their appearance and Healing Factor also invoke the Regenerador from Resident Evil 4 and the White Molded from Resident Evil 7: biohazard's "Not a Hero" DLC..