Going off the Chronology, these are the Thenardier-involving chapters that have portions done during exile while taking part in the pre-exile narrative (which ends with Gavroche profound calculator of distances):
Book 4, chapters 1 and 2 are from exile, chapter 3 has edits in exile. (first two chapters are an expansion of a page from before exile; chapter 3 has several edits, including the entire paragraph on how important it is being 5 years old)
All of Waterloo, including the final chapter
Book 3, chapter 1 has edits (dialogue from customers), chapter 2 is wholly exile, chapter 3 has edits (first 3 paragraphs are post-exile), chapters 5 (the long description of the forest as apocalypse), 6 (a couple sentences description of the former preceptor and the paragraphs about telling time by the king), 7 (adds Cosette's line "I don't think I ever had one" [a mother]), 8 (Mme T consults her husband with a look, but dialogue pre-existing, Cosette was nearly 8 but barely looked 6, the paragraph on Cosette's fear coming over her again, last sentence in the paragraph where Cosette jumps back in her hole after Valjean "finds" the lost money), 9 (next to last paragraph added)
Book 8, chapter 1 has edits (but it's all Marius and M. Leblanc), chapter 4 (heavily worked, no details), 5 (paragraphs 4-6 added which are all about Éponine, 6 (adds paragraph after list of battles, adds paragraph that ends with inscription from Ducray-Duminil, adds the line about the probable volume of the same novel on the floor, adds last two paragraphs of Azelma description, adds from "the man grumbled" to the end of the chapter), chapter 9 (adds first paragraph, adds into Thenardier's rant about the girls from "they have a father" to "do you know what's going to happen tomorrow"), 10 (work on the "Marius fails to hail a cab" section), chapter 14 (adds from "we must have a little Patron-Minette over there" to "I know the wreck"), chapter 16 (adds the verse Éponine sings), 17 (adds the paragraph on the stove giving off no odor and the one on the breath of air dissipating the scent of the stove), chapter 19 (adds the paragraph of Thenardier getting up to get his tavern sign but that takes the place of a previous description of the sign) 20 (general edits to first paragraph, adds the five lines of dialogue about Parnasse's whereabouts, adds "the painting you just saw, which could have been by David" up to "let's finish" in the same paragraph, adds the paragraphs "The master's painting" and the following one of Marius able to see it, adds paragraph on "One of the 'smokers'", adds paragraph "it was evidently an inaccessible soul in astonishment", adds paragraph "It was evident Thenardier avoided naming the girl", adds the two sentences beginning "the hideous and delicate products" and ending with "Villon"), 21 (adds from "The six captured bandits" to "and no one leave!"), 22 (adds "The old woman, stifled with indignation" to Gav's statement that her sort of beauty doesn't appeal to him, edits Gav's song, general edits from "came clamouring after him" to end of chapter).
Book 6, chapter 1 is exile, chapters 2 (Gav had originally been pulled in by Claquesous rather than Parnasse, the rest of this chapter is Gav, Parnasse and momes, no Thenardier references), 3 (changes some bandit names around and adds Parnasse, adds the descriptive paragraph on Brujon, adds the paragraph "One cannot always account for the wonders of escape".)
Book 8, chapter 4 is the key one, it has edits (bandit names changed, adds Éponine's full dialogue lines starting "I only have to shout", adds from "While leaving, Montparnasse murmured" to Thenardier's reply "Pardi") (the other chapters are just Marius and Cosette)
The little boys don't become Gav's brothers/Thenardier's sons until 1860, thus the addition of that chapter during the exile period, but they were pre-existing characters. In essence, these existing unfortunate children were assigned to Thenardier in 1860.
But as you can see from these edits in the chronology, Thenardier's actions were fully formed by February 1848. Edits to the chapters in which he takes part don't affect him. The important bits are the descriptions added during exile, so that would be where you'd want to concentrate if looking for clues as to where Hugo might have developed something of this nature after realising Thenardier was the character on which he could do this. But definitely beware of where you pull your evidence, since the stuff Thenardier does, rather than the stuff about him, is pre-exile.
What kind of literature and what kind of life is the same question. - Tom Stoppard