Postulated sequence of events tracing the time, place, and duration of formation of the main compositional classes of small bodies (top) to present-day observed characteristics (bottom; vertical spread reproducing roughly the distribution of orbital inclinations). The accretion duration is shown as gradient boxes ending at the fully formed bodies. This graph is adapted from Vernazza & Beck (2017) and Neveu & Vernazza (2019) with the following novelty: we highlight the possibility that so-called IDP-like C-types could be intrinsically related to IDP-like P- and D-type asteroids, representing different layers of a same body (C: core; P/D: outer shell). Therefore, C, P, and D-types may all have the same origin in the primordial trans-Neptunian disk. Kuiper belt objects (KBOs) that were implanted inward of the snowline following giant planet migration may have lost their P/D outer shell due to water ice sublimation revealing their C-type interiors.