  Type IIb supernovae (SNe IIb) present a unique opportunity for investigating
the evolutionary channels and mechanisms governing the evolution of
stripped-envelope SN progenitors due to a variety of observational constraints
available. Comparison of these constraints with the full distribution of
theoretical properties not only help ascertain the prevalence of observed
properties in nature, but can also reveal currently unobserved populations. In
this follow-up paper, we use the large grid of models presented in Sravan et
al. 2019 to derive distributions of single and binary SNe IIb progenitor
properties and compare them to constraints from three independent observational
probes: multi-band SN light-curves, direct progenitor detections, and
X-ray/radio observations. Consistent with previous work, we find that while
current observations exclude single stars as SN IIb progenitors, SN IIb
progenitors in binaries can account for them. We also find that the
distributions indicate the existence of an unobserved dominant population of
binary SNe IIb at low metallicity that arise due to mass transfer initiated on
the Hertzsprung Gap. In particular, our models indicate the existence of a
group of highly stripped (envelope mass ~0.1-0.2 M_sun) progenitors that are
compact (<50 R_sun) and blue (T_eff <~ 10^5K) with ~10^4.5-10^5.5 L_sun and low
density circumstellar mediums. As discussed in Sravan et al. 2019, this group
is necessary to account for SN IIb fractions and likely exist regardless of
metallicity. The detection of the unobserved populations indicated by our
models would support weak stellar winds and inefficient mass transfer in SN IIb
progenitors.
