In this chapter, we are given genealogies of the final six tribes.
I want to take a moment to point out that Zebulun and Dan are not given tribal genealogies. This is possibly because they were wiped out in the Assyrian exile. I tried counting the genealogical lists in the last couple chapters and there are only eleven distinct tribes described in chapters 2-7. Twelve is a significant number in Jewish thought, and the discrepancy is made up by listing the half tribes of Manasseh twice (i.e. the eastern half of Manasseh is listed in chapter 5 and the western half is listed here in chapter 7), making a total of twelve.
With that said, it should be pretty clear that the genealogies of these tribes are much abbreviated compared to Levi and Judah. While the previous chapter had 81 verses for Levi alone, this chapter has 40 verses for six tribes. The next chapter has additional genealogies for Benjamin, but for the other five tribes this is all they get. The entire tribe of Naphtali is described with a single verse. I think this chapter is listing the six tribes for the sake of completeness rather than because of the Chronicler's genuine interest.
We can also distinguish between two different kinds of genealogies in this chapter. Issachar, Benjamin and Asher are genealogies derived from military censuses. We know this because they have official counts of "fighting men" as well as the term "heads of families" (NIV) that can also be used to indicate "leader of a company", i.e. a military unit. Family trees are often co-opted in the bible into a parallel military organization (for instance, see Numbers 1-2), and for that reason genealogies can serve a double purpose as a military census, and vice versa. From the military terms, it is very likely that these three genealogies are copied from some other military census. Interestingly, v. 2 refers to these men as "during the reign of David" suggesting that the data may be coming from David's census in 2 Samuel 24.
On the other hand, Manasseh, Ephraim and possibly Naphtali are all derived from non-military sources because e.g. they do not count the number of men in these tribes and do not list any "heads of families" or leaders over these tribes. I think this is really cool because this is one of the simplest and most obvious examples of how we can distinguish between original sources that are feeding into the Chronicler's genealogy and from this we can tell that the Chronicler is actually patching together a collection of prior sources to write both this genealogy and his subsequent narrative.
Another example of this sort of discrepancy is that the genealogy of Joshua (v. 20-26) contains ten generations between Ephraim and Joshua, while the genealogy of Moses in chapter 6 presents three generations between Levi and Moses. This is a considerable difference since Ephraim and Levi are contemporaries, and Joshua and Moses are contemporaries as well. The ten generations between Ephraim and Joshua is plausible, while the three generations between Levi and Moses is very likely syncopated, and the difference between these two parallel genealogies may also signify that they come from different sources.
We can also find differences in the lists of Benjamin's sons. Verse 6 gives us three sons of Benjamin, 1 Chron 8:1-2 (the next chapter) lists five sons of Benjamin, and Gen 46:21 describes ten sons of Benjamin. Even the names are different amongst these lists. While it may be possible to study the names in depth and find some kind of pattern, for our purposes it's sufficient to note that each different arrangement of Benjamin's sons likely indicates a distinct genealogical source, and Chronicles contains two of them (neither of which are taken from Genesis alone).
The genealogy of Manasseh is also unusual because it includes references to several women: Maacah (Makir's sister or wife - v. 15 and 16 give different accounts of Maacah) and the daughters of Zelophehad (the same Zelophehad from Numbers 27). This is uncommon but not unheard of (for instance, the punchline of the entire book of Ruth is that she is part of David's genealogy). I'm not really sure that I could explain why this genealogy has so many women, but I do think it plausibly indicates yet another distinct source for the Chronicler's material. Ephraim and Asher both refer to a handful of woman as well (v. 24, 30, 32).
Although some parts of this genealogy are copied from elsewhere, large sections of this chapter are also unique to the OT. I don't think this represents original research by the Chronicler, however. It's much more likely that the Chronicler is copying from some unknown or lost original source.
Having established that there are both military and non-military sources in this chapter, and having established the strong probability that this genealogy is copied from prior sources and not original, there is another significant observation that we can make. The genealogies and particularly the military censuses of the northern tribes like Issachar and Asher must almost certainly predate the division of the kingdom of Israel in the time of Rehoboam. The divided kingdom is unlikely to have unified records, especially sensitive military records. After the division of the kingdom, most of the records of the northern kingdom would have been kept in Samaria and almost certainly would have been destroyed when Samaria was burned by the Assyrians. Chronicles must be primarily derived from records from Jerusalem, which was the capital of the united kingdom and after the split, the southern kingdom. Jerusalem was also sacked by the Babylonians, but since the Chronicler is also from Judah he would be far more likely to have access to the royal archives of Judah than the hated Samaritans.
We can even find hints of these differences in the length of the genealogies. The genealogy of Judah goes all the way through to the Babylonian exile, the genealogy of Simeon (who was a southern tribe) makes reference to Hezekiah (a king who lived well after the division between north and south, 1 Chron 4:41), the genealogy of Levi goes all the way through the Babylonian exile, but every other tribe has a genealogy that goes no further than Saul. 1 Chron 5:17 says that the genealogy of the Gadites was entered "during the reigns of Jotham... and Jeroboam", but it's a sparse genealogy with very little information, in keeping with the conflict between these two nations at the time.
Lastly, as a minor note, verse 21 gives us a sense of the enduring conflict between Israel and the Philistines. Even in the time of Jacob and Ephraim, two of Ephraim's own sons died while they were attacking Gath to steal livestock.