
I mean it could be because the manhwa didn't include some parts of the novel that it could be seen as inconsistent. But anyway, all the memories didn't instantly return to him right when he possessed the body, but gradually came as time went by. We aren't even shown which or how many memories of Hajeong's uncle did he remember

Sorry to say but I think the uncle introduced himself. He said something along the lines of "how dare you ignore your uncle". That's how mc knew he was the uncle I think. And with the violent tendencies and insistent calls from the uncle I think it should be somewhat safe to infer that uncle is indeed the source of his monetary problems.
From my understanding he did not "know" anything from "absorbing memories of his host body". I did not get the impression that he knew anything beforehand at all. He learned on the spot and adapted quickly. And I believe others got this impression as well.

Not really sure if we are reading the same dialogue. Im also referring to the dialogue. Lemme write out what I see in chapter 20:
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*As MC walks out of store*
???: There you are, you son of a bitch!" *Grabs hair* "Kang Ha Jeong!! How dare you ignore YOUR UNCLE! I was right to wait around the base!
Kang Ha Jeong: What? Let go of me!
???: I raised you because you are my NEPHEW, and this is how you repay me!! Did you get a boyfriend or something? This month's PAYMENT is way overdue!! GIVE ME MY MONEY, you brat!
Kang Ha Jeong thinks: Uncle? Nephew...? The NORTH SECURITY GATE did mention an uncle... So this must be (OG)'s uncle? He must have been looking for me since I didn't send him money this month...!!
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As you can see, EVERYTHING that MC had known could definitely have been inferred from what the uncle was saying. The story even clearly shows MC's thought process for the story to flow logically. MC clearly did not know who the uncle was before he started rambling about himself.
I really do not see what you mean by, and I am quoting you, "MC knew exactly who his uncle was from somehow absorbing memories of his host body". The dialogue COMPLETELY supports what I was saying.

Chapter 6 (internal monologue MC)
“What the hell”…. “Where on Earth is he sending all this money..?”
“Kang Jiseong 2.5 million, Kang Jiseong 3.8 million, Kang Jiseong 6.21 million”
“So that’s why he has no money!”
“But who is Kang Jiseong for him to send so much money every month?”
Chapter 19 (internal monologue MC)
“Obviously it’s not ‘Colonel Kang’s’ Hajeong’s family. Not that I have any living relatives anyway.”
“This must be ‘Sergeant Kang Hajeong’s’ uncle.”
“Has it happens I can remember sergeant Kang’s past as if it were my own. It’s not pleasant since it feels like a peeping Tom”
“Anyway I remember a few things about Kang’s Uncle, His legal Guardian. His name is Kang Byeonchan. He’s not a decent person”

Ah sorry about that, I thought you were referring to chapter 20. I got a bit heated when you said the plot is not consistent since I love the original work. Actually, the chapter 20 uncle pulling hair situation didn't happen in the original work I believe, that's why I thought you were referring to chapter 20 saying the readapted version messed up.
In the original the uncle was a very small plotpoint, only mentioned in one chapter. It was through a forced memory recollection (?). They also explain why MC was able to know about OG's past in general. Lemme try to dig it up for you:
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“You’re trash. If you’re going to try to kill yourself, shouldn’t you at least succeed once? How can you keep failing like this? What are you doing if not trying to get attention from others!”
I was lying still, wondering when this person would leave, thinking to myself that maybe I was being too harsh. As I tried to sit up again, a severe headache made me clutch my head.
With a metallic sound, someone’s memories flooded in. I could feel the guiding or psychic waves of the memories, most likely from Moohyuk’s pre-crash phase, mixed with similar wave frequencies—uncontrollable and chaotic.
Through the guiding wave of Sergeant Kang, I could glimpse some of the memories he had.
* * *
Kang Hajung was twenty years old and was thankful that he had a smooth jawline without any stubble. This was because he had no father to teach him how to shave.
His mother had run away long ago, and his father had been beaten to death in a gambling den. The one silver lining was that there was no gambling debt. Though his uncle, Kang Byeongchan, had tried to claim the life insurance money, Hajung was already over twenty, so he didn’t lose everything. Still, his uncle kept slowly nibbling away at Hajung’s money.
(Other sad stuff about uncle and MC's past)
***
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I guess there was a mistake by the manhwa authors while trying to make the manhwa more grounded in reality instead of just memory recollection. You should go read the novel instead it is really good. (=・ω・=)

Sorry to jump in the convo, but the hair pulling situation also happened in the novel. It was described that Hajeong was too shock to register the situation since it happened so suddenly to the point that it didn't even click to him even when 'Kang Hajeong's' uncle mentioned that he's his uncle the moment he grabbed his hair

Omg I think I found it. It seems that I have never read this chapter before and completely skipped it when I read it!!! Maybe I fat fingered the next chapter button or something.
No wonder I felt that something was amiss, I also thought it was strange that the manhwa was focusing so much on the uncle. I can't believe I would have read the entire novel while missing out on this chapter, thank you so much, you are a lifesaver!! ε=ε=(ノ≧∇≦)ノ

Yeah maybe I did forget, but still it's strange that I seem to remember reading Vol2 chapter 4 and 6, but have no recollection of 5. There's content about things other than the uncle in that chapter that I've missed too, so I really can't thank you enough.
I still am in genuine disbelief that I could have gone on to finish the novel without ever realising that I skipped a chapter. Like the novel is "ending" (as in all the translated chapters are gonna be released for free) in 3 months time, so after 3 months my connection with this novel might completely sever since I don't usually reread novels due to time.
At least now the damage is minimised and I only need to reread 10 chapters rather than 75% of the novel after everything releases. Or maybe this is a sign for me to start rereading novels in general. I hope you have a wonderful year ahead and everything goes well for you!(๑•ㅂ•)و✧

Yeah, I get you. It's a bit difficult to reread since I have a lot of stuff going on and my reading list is pretty long. It's quite fortunate that this one doesn't have many chapters and the story keeps drawing me in so all the wait is very worth it.
Thank you, I hope you stay in good health and everything goes well for you too
The exposition in this plot is not consistent at all. Just before MC knew exactly who his uncle was from somehow absorbing memories of his host body as well as having the knowledge that his uncle was the source of his lack of monetary funds. Yet chapters before MC had no knowledge of why his host body had such little funds available to him as well as in this chapter MC assuming his who his uncle was only after being provided outside information. It’s not consistent at all.