With a blank input applied, in otherwords the sync must be present but
no or little video, take a 5K ohm 2W resistor and temporarily short the
R,G, and B cathode to ground while looking at the screen in a mirror.
If the green is clearly much weaker than the red and blue, the tube is
confirmed low green emission.

On a Sony you would have to monitor the AKB return pulse from each
cathode on a cold start of the tube, tube off for at least 15 minutes.

I would guess that the prior owner had the blinking video at turn on
due to the unbalanced guns and the G2 voltage was increased to
compensate so the picture would be visible. This is pretty common on
the older 32" and 35" low end Sony (non-xbr) tubes from about 8 years
ago.