  The rate of oxygen formation determines the C/O ratio during stellar helium
burning. It is the single most important nuclear input of stellar evolution
theory including the evolution of Type II and Type Ia supernova. Yet the low
energy cross section of the fusion of 4He + 12C denoted as the 12C(a,g)16O
reaction still remains uncertain after forty years of extensive work. We
analyze and critically review the most recent measurements of complete angular
distributions of the outgoing gamma-rays at very low energies (Ecm > 1.0 MeV).
Our analysis of the angular distribution measured with the EUROGAM/GANDI arrays
lead us to conclude considerably larger error bars than published hence they
are excluded from the current sample of "world data". We show that the current
sample of "world data" of the measured E2 cross section factors below 1.7 MeV
cluster to two distinct groups that lead to two distinct extrapolations of
SE2(300) ~ 60 or ~ 154 keVb. We point to a much neglected discrepancy between
the measured E1-E2 phase difference (phi_12) and unitarity as required by the
Watson theorem, suggesting systematic problem(s) of some of the measured
gamma-ray angular distributions. The ambiguity of the extrapolated SE2(300)
together with a previously observed ambiguity of SE1(300) represent the current
state of the art of the field and they must be resolved by future measurements
of complete and detailed angular distributions of the 12C(a,g) reaction at very
low energies (Ecm < 1.0 MeV).
