This is a gr9 question! NOT an easy answer. And I think you got your question across just fine 😉

AR deserves more credit* than you might think, for the way she jumps around through the series, shedding light on the previously established timeline via different POVs, or just having a character revisit the same scene. Sometimes she also does “Retroactive continuity,” or “retcon” for short: “the alteration of previously established facts in the continuity of a fictional work.”

*Actually, some might argue that when she does this it offers frustratingly conflicting views on previous events, hence, the Unreliable Narrator issues we have throughout the VC.

Anon: “…as much as I love these vamps I feel like

gradual character development isn’t really present, it seems to come suddenly and all at once instead.”

So here’s the thing, in the VC, the publication dates of the books ARE NOT NECESSARILY aligned with the chronological timeline of the set of stories described in the books. (This Timeline I found seems pretty accurate.)

1. IWTV (published 1976) lays out Louis’ story (between approx. 1791 – 1975).
2. TVL (published 1985) is Lestat’s story (between

   approx.

   1766 – 1985) plus the origin story of the vampires (Ancient Egyptian times,

   approx.

   4000 BC). 

3. QOTD (published 1998) is Lestat’s story in 1985, it was a whirlwind Bad Romance.
4. TOBT

   (published 1992) is Lestat’s Body Dysmorphic Disorder episode, takes place in 1991.

• And so on…

TL;DR, I see clear character development when I take in the larger view of all the stories. Some of the later canon books I might have preferred not to have happened, but OH WELL.

But character development in fictional characters (as with actual real people) =/= a clean line of improvement or deterioration. Lestat and Armand have both improved over time in many ways, but they’ve also lost good qualities. Lestat’s definitely lost a few marbles along the way.

Hit the jump for a little more, & spoilers.

For brevity, just gonna answer your question re: 
“how the vamps change overtime, character wise? For example, say Lestat in TVL vs Lestat in body thief? Or even Armand in IWTV vs Armand in the later books.”

Lestat: 

TVL!Lestat is feisty, freshly resurrected, appetite for destruction, wants to “correct the record” of IWTV by sharing the secrets that he couldn’t in IWTV, and establish himself as the actual protagonist of the series. 

Approx. 10 years later in the timeline of the books, TOBT!Lestat is suffering emotionally from the blowback of what happened after sharing that information and trying to be a big shot, and he’s got ghost!Claudia on his back prodding him to consider whether he even deserves to continue vampiring ;A; when he’s so weak against his own impulses. He tries to suicide, and when that doesn’t work, has a renewed sense of belonging in the world. Then in TOBT, he fucks up pretty royally, relies on one best friend to help him get things back to normal, and then almost destroys that friendship by selfishly Forced-Dark-Gift-paying-it-forward. So I’d say that’s a lot of character development.

Armand:

IWTV!Armand was supposed to be intimidating and shrouded in mystery, the teacher/mentor for Louis that Lestat refused to be. Later, when we get Armand’s backstory in TVL, TVA, and B&G, we see his origins and how he got to be the manager of the Theatre Des Vampires, and however intimidating he might have been to Louis, that wasn’t remotely close to what he was like as the leader of the Children of Darkness, Parisian Chapter. So he’s had to adapt to alot of harsh situations, and find some sense of inner peace along the way. 

Lestat and Armand are almost 2 sides of the same coin; Lestat was forced into the Dark Gift, Armand begged for it. Lestat had to learn how to vampire alone as an orphan, Armand had an overbearing teacher and was then kidnapped by a cult. 

They’ve both had to deal with finding peace and a place for themselves in a world that doesn’t really need or want them, a struggle many of us readers can identify with as being part of our own character development over time.