Vbe is defined (by photocurrent vs the B-E diode I-V),
it is merely not observable. Vce is directly observable
and you could in under an hour characterize Tr vs
Vce @ Ic, I'm sure. As a rule there is not that much
difference between Vbe and Vbc, 100mV or so, and
you can figure letting Vce get below 200mV is putting
you too close for comfort.
Without base terminal access you have no path to
remove stored charge smartly. That's the real issue.
So don't store any more than you really, really need.
Unfortunately the variability of current transfer coefficient
and degradation over life (let alone any environmental
unpleasantness) tends to make people pack heavy...
too dark is one corner of the box, too slow turning off
is another.