There are so many factors which influence the basic tuning of a theremin, including aging of the components, that there are no general rules.
The only visible parameter is the fact that you'll discover one day that you can't set up your theremin because you reach the clockwise or counterclockwise end of the pitch or volume tuning potentiometer without obtaining the ideal setting.
The hell is when it worked still at home but does surprisingly not longer work in a different environment, for example on stage, 15 minutes before the gig starts, due to different temperature, humidity, grounding, etc.
That's why I teach "Theremin first aid" at theremin festivals in Europe. I help people to detect and to understand what goes wrong, why it goes wrong and how to fix it rapidly, at least in a rough-and-ready way, so that there is no more reason to panic before a gig.
The red plastic tool is your friend!