[time-nuts] What interrupts aging?

[John Ackermann N8UR]

We know of OCXO that have been continuously running for years and have 
exceptional aging, supposedly as a result.

What does it take to interrupt that? A momentary loss of power?  The 
oven cooling down?  Some long period of off-time?  Or, once the 
oscillator has baked in will it return to that low aging once it has 
been powered up and thermally stabilized?

John