2025ApJ...990...60F

We present a comprehensive analysis of 32 type II supernovae (SNe II) with plateau phase photometry and late phase (nebular) spectroscopy available, aiming to bridge the gap between the surface and core of their red supergiant (RSG) progenitors. Using MESA+STELLA, we compute an extensive grid of SN II light-curve models originating from RSG with effective temperatures T_eff around 3650 K and hydrogen-rich envelopes artificially stripped to varying degrees. These models are then used to derive the hydrogen-rich envelope masses M_Henv for SNe II from their plateau phase light curves. Nebular spectroscopy further constrains the progenitor RSG's luminosity log L_prog and is employed to remove the degeneracies in light-curve modeling. The comparison between log L_prog-M_Henv reveals that M_Henv spans a broad range at the same log L_prog, and almost all SNe II have lower M_Henv than the prediction of the default stellar wind models. We explore alternative wind prescriptions, binary evolution models, and the possibility of more compact RSG progenitors. Although binary interaction offers a compelling explanation for the nonmonotonicity and large scatter in the log L_prog-M_Henv relation, the high occurrence rate of partially stripped RSGs cannot be accounted for by stable binary mass transfer alone without fine-tuned orbital parameters. This highlights that, despite being the most commonly observed class of core-collapse SNe, SNe II likely originate from a variety of mass-loss histories and evolutionary pathways that are more diverse and complex than typically assumed in standard stellar evolution models.