I have some very high resolution data showing voltage on a D/Y 230kV to 13800 (nominal taps) as well as load, reactive power, etc. I show RMS voltage at the substation secondary moving between 13,440 (4 taps below nominal) and 13,890 (one tap above nominal) in the presence of gently varying load. Thing is I can't point to actual tap change events. What I think is that even though the voltage is varying (because of power flow), i don't think I have a single tap change event recorded. Does this sound about right?

Can you post your high resolution data ?

Wish I could. I don't think you can post pictures, unfortunately. However, if you installed my software (freely available) you could look at it. I had a buddy show me a verified tap change though in the last hour, it makes a clear RMS "instantaneous" voltage step on a millisecond time scale, with corresponding current change. And the voltage waveforms are notched for several cycles. So I think I know what to look for now, and the data I have doesn't have any of those, so I think it was just load changes forcing the voltage up and down through about 6 taps worth of voltage, even though the tap didn't change over the recorded duration.