What about worlds in, say, the Marches where they're described as initially populated by Imperial settlers? It seems straightforward to me that the 3I grabbed some systems, allocated them to nobles to oversight, set an administration in place (govt type 6, 8 or 9, possibly evolving through these) and there's another world providing a greater revenue base for the 3I. Would somewhere like Jewell be one of these?
Here we get into interpretation of very scanty evidence. Worlds like Mora, Regina and Fornice were settled before the turn of the 1st Century. Some of the other worlds in Trin's Veil and Lunion seem very likely to have been settled early as well. Major inroads in settling the Spinward Marches is said to have been done by 200 [TTB:149]
And yet, the major Imperial expansion and settlement of the Spinward Marches is said to take place from 200-400 [TD18:23].
My explanation for that seeming contradiction is that prior to 200, settlers from the Imperium were commercial ventures like Mora and utopian settlers trying to get AWAY from the Imperium (plus a number of groups expelled from the Imperium during the Pacification Campaigns). Up until 200 only a handful of worlds join the Imperium, and mostly on their own initiative. Then, around 200, Martin II decides to integrate the scattered worlds behind The Claw (that's why he launched the Vargr Campaigns -- to secure the route).
Note that Regina is settled in 75 but doesn't join the Imperium until 250 (same with the other worlds in the Regina Cluster, which have mostly joined by 300).
So
my take is that most of the nice colonization goals in the Marches (and some of the not-so-nice colonization goals -- some of the Pacification Campaign exiles were dumped with little consideration, depending on who exactly did the dumping) were settled long before the Imperium took an interest in them.
Also, and this is very much my own take, not even as scantily supported as the preceding bit, I think the Imperium is suppose to defend the autonomy of member worlds and to protect them against undue influence from anyone. No doubt, human nature being what it is, it has failed on more than one occasion, but that's what it is supposed to do.
Hans